W32.Gaobot.WO

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Discovered: April 06, 2004
Updated: February 13, 2007 12:21:01 PM
Also Known As: Backdoor.Agobot.lh [Kaspersky], W32/Gaobot.worm.gen.g [McAfee]
Type: Worm
Systems Affected: Windows



W32.Gaobot.WO is a variant of W32.Gaobot.gen. It attempts to spread through network shares that have weak passwords. It also allows attackers to access an infected computer through a predetermined IRC channel.

The worm uses multiple vulnerabilities to spread, including:


W32.Gaobot.WO is packed with FSG.


Note: Virus definitions version 60404al (extended version 4/4/2004 rev. 38) detect this threat as W32.HLLW.Gaobot.gen.


Antivirus Protection Dates

  • Initial Rapid Release version April 07, 2004
  • Latest Rapid Release version August 20, 2008 revision 017
  • Initial Daily Certified version April 07, 2004
  • Latest Daily Certified version August 20, 2008 revision 016
  • Initial Weekly Certified release date April 07, 2004

Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

Writeup By: Hiroshi Shinotsuka

Discovered: April 06, 2004
Updated: February 13, 2007 12:21:01 PM
Also Known As: Backdoor.Agobot.lh [Kaspersky], W32/Gaobot.worm.gen.g [McAfee]
Type: Worm
Systems Affected: Windows



When W32.Gaobot.WO is executed, it performs the following actions:

  1. Copies and executes itself as %System%\Netlink32.exe.


    Note: %System% is a variable. The worm locates the System folder and copies itself to that location. By default, this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).


  2. Adds the value:

    "NetLink"="netlink32.exe"

    to the registry keys:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\
    RunServices

    so that the worm runs when you start Windows.

  3. Ends the processes that are associated with antivirus and firewall software. Refer to "Processes" at the end of this section for a list of the process names.

  4. Attempts to end the following processes, which are associated with other worms:
    • taskmon.exe
    • bbeagle.exe
    • d3dupdate.exe
    • winsys.exe
    • ssate.exe
    • i11r54n4.exe
    • rate.exe
    • irun4.exe
    • Ssate.exe

  5. Appends the following lines to the infected computer's hosts file:

    127.0.0.1 www.trendmicro.com
    127.0.0.1 trendmicro.com
    127.0.0.1 rads.mcafee.com
    127.0.0.1 customer.symantec.com
    127.0.0.1 liveupdate.symantec.com
    127.0.0.1 us.mcafee.com
    127.0.0.1 updates.symantec.com
    127.0.0.1 update.symantec.com
    127.0.0.1 www.nai.com
    127.0.0.1 nai.com
    127.0.0.1 secure.nai.com
    127.0.0.1 dispatch.mcafee.com
    127.0.0.1 download.mcafee.com
    127.0.0.1 www.my-etrust.com
    127.0.0.1 my-etrust.com
    127.0.0.1 mast.mcafee.com
    127.0.0.1 ca.com
    127.0.0.1 www.ca.com
    127.0.0.1 networkassociates.com
    127.0.0.1 www.networkassociates.com
    127.0.0.1 avp.com
    127.0.0.1 www.kaspersky.com
    127.0.0.1 www.avp.com
    127.0.0.1 kaspersky.com
    127.0.0.1 www.f-secure.com
    127.0.0.1 f-secure.com
    127.0.0.1 viruslist.com
    127.0.0.1 www.viruslist.com
    127.0.0.1 liveupdate.symantecliveupdate.com
    127.0.0.1 mcafee.com
    127.0.0.1 www.mcafee.com
    127.0.0.1 sophos.com
    127.0.0.1 www.sophos.com
    127.0.0.1 symantec.com
    127.0.0.1 securityresponse.symantec.com
    127.0.0.1 www.symantec.com

  6. Connects to a predetermined IRC channel, using its own IRC client, and listens for commands.

    The worm can:
    • Take a screenshot of the system
    • Change the IRC server to which the worm connects
    • Force a connection to a specified IRC channel
    • Terminate the worm
    • Have the worm send messages to people or channels on IRC
    • Instruct the worm to send files from the system to the specified user over IRC (DCC Send)
    • Download and execute files
    • Steal system information
    • Harvest email addresses
    • Steal CD keys for various games
    • Connect to FTP servers to upload files
    • Terminate processes (other than those mentioned in step 4)
    • Connect to other systems using SSH
    • Run the worm as a SOCKS proxy server and make connections. These connections will then appear to have come from an infected computer instead of the attacker.

  7. Attempts to spread to other computers by exploiting the following vulnerabilities:
  8. Uses various user names and weak passwords. It also uses the user names found using NetUserEnum() to probe these shares:
    • admin$
    • ipc$
    • c$
    • d$
    • e$

  9. Copies itself to any computers it compromised using the previously mentioned exploits.

  10. If you go to www.paypal.com, it tries to steal PayPal login information by logging keystrokes. The worm can also be instructed to steal login information for several AOL services, including AOL Instant Messenger service (AIM).


Processes
W32.Gaobot.WO attempts to end the following processes:
  • _AVP32.EXE
  • _AVPCC.EXE
  • _AVPM.EXE
  • ACKWIN32.EXE
  • ADAWARE.EXE
  • ADVXDWIN.EXE
  • AGENTSVR.EXE
  • AGENTW.EXE
  • ALERTSVC.EXE
  • ALEVIR.EXE
  • ALOGSERV.EXE
  • AMON9X.EXE
  • ANTI-TROJAN.EXE
  • ANTIVIRUS.EXE
  • ANTS.EXE
  • APIMONITOR.EXE
  • APLICA32.EXE
  • APVXDWIN.EXE
  • ARR.EXE
  • ATCON.EXE
  • ATGUARD.EXE
  • ATRO55EN.EXE
  • ATUPDATER.EXE
  • ATWATCH.EXE
  • AU.EXE
  • AUPDATE.EXE
  • AUTODOWN.EXE
  • AUTO-PROTECT.NAV80TRY.EXE
  • AUTOTRACE.EXE
  • AUTOUPDATE.EXE
  • AVCONSOL.EXE
  • AVE32.EXE
  • AVGCC32.EXE
  • AVGCTRL.EXE
  • AVGNT.EXE
  • AVGSERV.EXE
  • AVGSERV9.EXE
  • AVGUARD.EXE
  • AVGW.EXE
  • AVKPOP.EXE
  • AVKSERV.EXE
  • AVKSERVICE.EXE
  • AVKWCTl9.EXE
  • AVLTMAIN.EXE
  • AVNT.EXE
  • AVP.EXE
  • AVP32.EXE
  • AVPCC.EXE
  • AVPDOS32.EXE
  • AVPM.EXE
  • AVPTC32.EXE
  • AVPUPD.EXE
  • AVSCHED32.EXE
  • AVSYNMGR.EXE
  • AVWIN95.EXE
  • AVWINNT.EXE
  • AVWUPD.EXE
  • AVWUPD32.EXE
  • AVWUPSRV.EXE
  • AVXMONITOR9X.EXE
  • AVXMONITORNT.EXE
  • AVXQUAR.EXE
  • BACKWEB.EXE
  • BARGAINS.EXE
  • BD_PROFESSIONAL.EXE
  • BEAGLE.EXE
  • BELT.EXE
  • BIDEF.EXE
  • BIDSERVER.EXE
  • BIPCP.EXE
  • BIPCPEVALSETUP.EXE
  • BISP.EXE
  • BLACKD.EXE
  • BLACKICE.EXE
  • BLSS.EXE
  • BOOTCONF.EXE
  • BOOTWARN.EXE
  • BORG2.EXE
  • BPC.EXE
  • BRASIL.EXE
  • BS120.EXE
  • BUNDLE.EXE
  • BVT.EXE
  • CCAPP.EXE
  • CCEVTMGR.EXE
  • CCPXYSVC.EXE
  • CDP.EXE
  • CFD.EXE
  • CFGWIZ.EXE
  • CFIADMIN.EXE
  • CFIAUDIT.EXE
  • CFINET.EXE
  • CFINET32.EXE
  • Claw95.EXE
  • CLAW95CF.EXE
  • CLEAN.EXE
  • CLEANER.EXE
  • CLEANER3.EXE
  • CLEANPC.EXE
  • CLICK.EXE
  • CMD32.EXE
  • CMESYS.EXE
  • CMGRDIAN.EXE
  • CMON016.EXE
  • CONNECTIONMONITOR.EXE
  • CPD.EXE
  • CPF9X206.EXE
  • CPFNT206.EXE
  • CTRL.EXE
  • CV.EXE
  • CWNB181.EXE
  • CWNTDWMO.EXE
  • DATEMANAGER.EXE
  • DCOMX.EXE
  • DEFALERT.EXE
  • DEFSCANGUI.EXE
  • DEFWATCH.EXE
  • DEPUTY.EXE
  • DIVX.EXE
  • DLLCACHE.EXE
  • DLLREG.EXE
  • DOORS.EXE
  • DPF.EXE
  • DPFSETUP.EXE
  • DPPS2.EXE
  • DRWATSON.EXE
  • DRWEB32.EXE
  • DRWEBUPW.EXE
  • DSSAGENT.EXE
  • DVP95.EXE
  • DVP95_0.EXE
  • ECENGINE.EXE
  • EFPEADM.EXE
  • EMSW.EXE
  • ENT.EXE
  • ESAFE.EXE
  • ESCANH95.EXE
  • ESCANHNT.EXE
  • ESCANV95.EXE
  • ESPWATCH.EXE
  • ETHEREAL.EXE
  • ETRUSTCIPE.EXE
  • EVPN.EXE
  • EXANTIVIRUS-CNET.EXE
  • EXE.AVXW.EXE
  • EXPERT.EXE
  • EXPLORE.EXE
  • F-AGNT95.EXE
  • F-AGOBOT.EXE
  • FAMEH32.EXE
  • FAST.EXE
  • FCH32.EXE
  • FIH32.EXE
  • FINDVIRU.EXE
  • FIREWALL.EXE
  • FLOWPROTECTOR.EXE
  • FNRB32.EXE
  • FPROT.EXE
  • F-PROT.EXE
  • F-PROT95.EXE
  • FP-WIN.EXE
  • FP-WIN_TRIAL.EXE
  • FRW.EXE
  • FSAA.EXE
  • FSAV.EXE
  • FSAV32.EXE
  • FSAV530STBYB.EXE
  • FSAV530WTBYB.EXE
  • FSAV95.EXE
  • FSGK32.EXE
  • FSM32.EXE
  • FSMA32.EXE
  • FSMB32.EXE
  • F-STOPW.EXE
  • GATOR.EXE
  • GBMENU.EXE
  • GBPOLL.EXE
  • GENERICS.EXE
  • GMT.EXE
  • GUARD.EXE
  • GUARDDOG.EXE
  • HACKTRACERSETUP.EXE
  • HBINST.EXE
  • HBSRV.EXE
  • HIJACKTHIS.EXE
  • HOTACTIO.EXE
  • HOTPATCH.EXE
  • HTLOG.EXE
  • HTPATCH.EXE
  • HWPE.EXE
  • HXDL.EXE
  • HXIUL.EXE
  • IAMAPP.EXE
  • IAMSERV.EXE
  • IAMSTATS.EXE
  • IBMASN.EXE
  • IBMAVSP.EXE
  • ICLOAD95.EXE
  • ICLOADNT.EXE
  • ICMON.EXE
  • ICSUPP95.EXE
  • ICSUPPNT.EXE
  • IDLE.EXE
  • IEDLL.EXE
  • IEDRIVER.EXE
  • IEXPLORER.EXE
  • IFACE.EXE
  • IFW2000.EXE
  • INETLNFO.EXE
  • INFUS.EXE
  • INFWIN.EXE
  • INIT.EXE
  • INTDEL.EXE
  • INTREN.EXE
  • IOMON98.EXE
  • IPARMOR.EXE
  • IRIS.EXE
  • ISASS.EXE
  • ISRV95.EXE
  • ISTSVC.EXE
  • JAMMER.EXE
  • JDBGMRG.EXE
  • JEDI.EXE
  • KAVLITE40ENG.EXE
  • KAVPERS40ENG.EXE
  • KAVPF.EXE
  • KAZZA.EXE
  • KEENVALUE.EXE
  • KERIO-PF-213-EN-WIN.EXE
  • KERIO-WRL-421-EN-WIN.EXE
  • KERIO-WRP-421-EN-WIN.EXE
  • KERNEL32.EXE
  • KILLPROCESSSETUP161.EXE
  • LAUNCHER.EXE
  • LDNETMON.EXE
  • LDPRO.EXE
  • LDPROMENU.EXE
  • LDSCAN.EXE
  • LNETINFO.EXE
  • LOADER.EXE
  • LOCALNET.EXE
  • LOCKDOWN.EXE
  • LOCKDOWN2000.EXE
  • LOOKOUT.EXE
  • LORDPE.EXE
  • LSETUP.EXE
  • LUALL.EXE
  • LUAU.EXE
  • LUCOMSERVER.EXE
  • LUINIT.EXE
  • LUSPT.EXE
  • MAPISVC32.EXE
  • MCAGENT.EXE
  • MCMNHDLR.EXE
  • MCSHIELD.EXE
  • MCTOOL.EXE
  • MCUPDATE.EXE
  • MCVSRTE.EXE
  • MCVSSHLD.EXE
  • MD.EXE
  • MFIN32.EXE
  • MFW2EN.EXE
  • MFWENG3.02D30.EXE
  • MGAVRTCL.EXE
  • MGAVRTE.EXE
  • MGHTML.EXE
  • MGUI.EXE
  • MINILOG.EXE
  • MMOD.EXE
  • MONITOR.EXE
  • MOOLIVE.EXE
  • MOSTAT.EXE
  • MPFAGENT.EXE
  • MPFSERVICE.EXE
  • MPFTRAY.EXE
  • MRFLUX.EXE
  • MSAPP.EXE
  • MSBB.EXE
  • MSBLAST.EXE
  • MSCACHE.EXE
  • MSCCN32.EXE
  • MSCMAN.EXE
  • MSCONFIG.EXE
  • MSDM.EXE
  • MSDOS.EXE
  • MSIEXEC16.EXE
  • MSINFO32.EXE
  • MSLAUGH.EXE
  • MSMGT.EXE
  • MSMSGRI32.EXE
  • MSSMMC32.EXE
  • MSSYS.EXE
  • MSVXD.EXE
  • MU0311AD.EXE
  • MWATCH.EXE
  • N32SCANW.EXE
  • NAV.EXE
  • NAVAP.NAVAPSVC.EXE
  • NAVAPSVC.EXE
  • NAVAPW32.EXE
  • NAVDX.EXE
  • NAVENGNAVEX15.NAVLU32.EXE
  • NAVLU32.EXE
  • NAVNT.EXE
  • NAVSTUB.EXE
  • NAVW32.EXE
  • NAVWNT.EXE
  • NC2000.EXE
  • NCINST4.EXE
  • NDD32.EXE
  • NEOMONITOR.EXE
  • NEOWATCHLOG.EXE
  • NETARMOR.EXE
  • NETD32.EXE
  • NETINFO.EXE
  • NETMON.EXE
  • NETSCANPRO.EXE
  • NETSPYHUNTER-1.2.EXE
  • NETSTAT.EXE
  • NETUTILS.EXE
  • NISSERV.EXE
  • NISUM.EXE
  • NMAIN.EXE
  • NOD32.EXE
  • NORMIST.EXE
  • NORTON_INTERNET_SECU_3.0_407.EXE
  • NOTSTART.EXE
  • NPF40_TW_98_NT_ME_2K.EXE
  • NPFMESSENGER.EXE
  • NPROTECT.EXE
  • NPSCHECK.EXE
  • NPSSVC.EXE
  • NSCHED32.EXE
  • NSSYS32.EXE
  • NSTASK32.EXE
  • NSUPDATE.EXE
  • NT.EXE
  • NTRTSCAN.EXE
  • NTVDM.EXE
  • NTXconfig.EXE
  • NUI.EXE
  • NUPGRADE.EXE
  • NVARCH16.EXE
  • NVC95.EXE
  • NVSVC32.EXE
  • NWINST4.EXE
  • NWSERVICE.EXE
  • NWTOOL16.EXE
  • OLLYDBG.EXE
  • ONSRVR.EXE
  • OPTIMIZE.EXE
  • OSTRONET.EXE
  • OTFIX.EXE
  • OUTPOST.EXE
  • OUTPOSTINSTALL.EXE
  • OUTPOSTPROINSTALL.EXE
  • PADMIN.EXE
  • PANIXK.EXE
  • PATCH.EXE
  • PAVCL.EXE
  • PAVPROXY.EXE
  • PAVSCHED.EXE
  • PAVW.EXE
  • PCC2002S902.EXE
  • PCC2K_76_1436.EXE
  • PCCIOMON.EXE
  • PCCNTMON.EXE
  • PCCWIN97.EXE
  • PCCWIN98.EXE
  • PCDSETUP.EXE
  • PCFWALLICON.EXE
  • PCIP10117_0.EXE
  • PCSCAN.EXE
  • PDSETUP.EXE
  • PENIS.EXE
  • PERISCOPE.EXE
  • PERSFW.EXE
  • PERSWF.EXE
  • PF2.EXE
  • PFWADMIN.EXE
  • PGMONITR.EXE
  • PINGSCAN.EXE
  • PLATIN.EXE
  • POP3TRAP.EXE
  • POPROXY.EXE
  • POPSCAN.EXE
  • PORTDETECTIVE.EXE
  • PORTMONITOR.EXE
  • POWERSCAN.EXE
  • PPINUPDT.EXE
  • PPTBC.EXE
  • PPVSTOP.EXE
  • PRIZESURFER.EXE
  • PRMT.EXE
  • PRMVR.EXE
  • PROCDUMP.EXE
  • PROCESSMONITOR.EXE
  • PROCEXPLORERV1.0.EXE
  • PROGRAMAUDITOR.EXE
  • PROPORT.EXE
  • PROTECTX.EXE
  • PSPF.EXE
  • PURGE.EXE
  • PUSSY.EXE
  • PVIEW95.EXE
  • QCONSOLE.EXE
  • QSERVER.EXE
  • RAPAPP.EXE
  • RAV7.EXE
  • RAV7WIN.EXE
  • RAV8WIN32ENG.EXE
  • RAY.EXE
  • RB32.EXE
  • RCSYNC.EXE
  • REALMON.EXE
  • REGED.EXE
  • REGEDIT.EXE
  • REGEDT32.EXE
  • RESCUE.EXE
  • RESCUE32.EXE
  • RRGUARD.EXE
  • RSHELL.EXE
  • RTVSCAN.EXE
  • RTVSCN95.EXE
  • RULAUNCH.EXE
  • RUN32DLL.EXE
  • RUNDLL.EXE
  • RUNDLL16.EXE
  • RUXDLL32.EXE
  • SAFEWEB.EXE
  • SAHAGENT.EXE
  • SAVE.EXE
  • SAVENOW.EXE
  • SBSERV.EXE
  • SC.EXE
  • SCAM32.EXE
  • SCAN32.EXE
  • SCAN95.EXE
  • SCANPM.EXE
  • SCRSCAN.EXE
  • SCRSVR.EXE
  • SCVHOST.EXE
  • SD.EXE
  • SERV95.EXE
  • SERVICE.EXE
  • SERVLCE.EXE
  • SERVLCES.EXE
  • SETUP_FLOWPROTECTOR_US.EXE
  • SETUPVAMEEVAL.EXE
  • SFC.EXE
  • SGSSFW32.EXE
  • SH.EXE
  • SHELLSPYINSTALL.EXE
  • SHN.EXE
  • SHOWBEHIND.EXE
  • SMC.EXE
  • SMS.EXE
  • SMSS32.EXE
  • SOAP.EXE
  • SOFI.EXE
  • SPERM.EXE
  • SPF.EXE
  • SPHINX.EXE
  • SPOLER.EXE
  • SPOOLCV.EXE
  • SPOOLSV32.EXE
  • SPYXX.EXE
  • SREXE.EXE
  • SRNG.EXE
  • SS3EDIT.EXE
  • SSG_4104.EXE
  • SSGRATE.EXE
  • ST2.EXE
  • START.EXE
  • STCLOADER.EXE
  • SUPFTRL.EXE
  • SUPPORT.EXE
  • SUPPORTER5.EXE
  • SVC.EXE
  • SVCHOSTC.EXE
  • SVCHOSTS.EXE
  • SVSHOST.EXE
  • SWEEP95.EXE
  • SWEEPNET.SWEEPSRV.SYS.SWNETSUP.EXE
  • SYMPROXYSVC.EXE
  • SYMTRAY.EXE
  • SYSEDIT.EXE
  • SYSTEM.EXE
  • SYSTEM32.EXE
  • SYSUPD.EXE
  • TASKMG.EXE
  • TASKMO.EXE
  • TASKMON.EXE
  • TAUMON.EXE
  • TBSCAN.EXE
  • TC.EXE
  • TCA.EXE
  • TCM.EXE
  • TDS2-98.EXE
  • TDS2-NT.EXE
  • TDS-3.EXE
  • TEEKIDS.EXE
  • TFAK.EXE
  • TFAK5.EXE
  • TGBOB.EXE
  • TITANIN.EXE
  • TITANINXP.EXE
  • TRACERT.EXE
  • TRICKLER.EXE
  • TRJSCAN.EXE
  • TRJSETUP.EXE
  • TROJANTRAP3.EXE
  • TSADBOT.EXE
  • TVMD.EXE
  • TVTMD.EXE
  • UNDOBOOT.EXE
  • UPDAT.EXE
  • UPDATE.EXE
  • UPGRAD.EXE
  • UTPOST.EXE
  • VBCMSERV.EXE
  • VBCONS.EXE
  • VBUST.EXE
  • VBWIN9X.EXE
  • VBWINNTW.EXE
  • VCSETUP.EXE
  • VET32.EXE
  • VET95.EXE
  • VETTRAY.EXE
  • VFSETUP.EXE
  • VIR-HELP.EXE
  • VIRUSMDPERSONALFIREWALL.EXE
  • VNLAN300.EXE
  • VNPC3000.EXE
  • VPC32.EXE
  • VPC42.EXE
  • VPFW30S.EXE
  • VPTRAY.EXE
  • VSCAN40.EXE
  • VSCENU6.02D30.EXE
  • VSCHED.EXE
  • VSECOMR.EXE
  • VSHWIN32.EXE
  • VSISETUP.EXE
  • VSMAIN.EXE
  • VSMON.EXE
  • VSSTAT.EXE
  • VSWIN9XE.EXE
  • VSWINNTSE.EXE
  • VSWINPERSE.EXE
  • W32DSM89.EXE
  • W9X.EXE
  • WATCHDOG.EXE
  • WEBDAV.EXE
  • WEBSCANX.EXE
  • WEBTRAP.EXE
  • WFINDV32.EXE
  • WGFE95.EXE
  • WHOSWATCHINGME.EXE
  • WIMMUN32.EXE
  • WIN32.EXE
  • WIN32US.EXE
  • WINACTIVE.EXE
  • WIN-BUGSFIX.EXE
  • WINDOW.EXE
  • WINDOWS.EXE
  • WININETD.EXE
  • WININIT.EXE
  • WININITX.EXE
  • WINLOGIN.EXE
  • WINMAIN.EXE
  • WINNET.EXE
  • WINPPR32.EXE
  • WINRECON.EXE
  • WINSERVN.EXE
  • WINSSK32.EXE
  • WINSTART.EXE
  • WINSTART001.EXE
  • WINTSK32.EXE
  • WINUPDATE.EXE
  • WKUFIND.EXE
  • WNAD.EXE
  • WNT.EXE
  • WRADMIN.EXE
  • WRCTRL.EXE
  • WSBGATE.EXE
  • WUPDATER.EXE
  • WUPDT.EXE
  • WYVERNWORKSFIREWALL.EXE
  • XPF202EN.EXE
  • ZAPRO.EXE
  • ZAPSETUP3001.EXE
  • ZATUTOR.EXE
  • ZONALM2601.EXE
  • ZONEALARM.EXE


Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
  • Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media.
  • Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.

Writeup By: Hiroshi Shinotsuka

Discovered: April 06, 2004
Updated: February 13, 2007 12:21:01 PM
Also Known As: Backdoor.Agobot.lh [Kaspersky], W32/Gaobot.worm.gen.g [McAfee]
Type: Worm
Systems Affected: Windows



The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

  1. Disable System Restore (Windows Me/XP).
  2. Restart the computer in Safe mode or VGA mode.
  3. Restore the Hosts file.
  4. Reverse the changes made to the registry, and then restart the computer.
  5. Update the virus definitions.
  6. Run a full system scan and delete all the files detected as W32.Gaobot.WO.
For details on each of these steps, read the following instructions.


Before you begin:
If you are running Windows NT/2000/XP, make sure that you do, or have done, the following:


1. To disable System Restore (Windows Me/XP)
If you are running Windows Me or Windows XP, we recommend that you temporarily turn off System Restore. Windows Me/XP uses this feature, which is enabled by default, to restore the files on your computer in case they become damaged. If a virus, worm, or Trojan infects a computer, System Restore may back up the virus, worm, or Trojan on the computer.

Windows prevents outside programs, including antivirus programs, from modifying System Restore. Therefore, antivirus programs or tools cannot remove threats in the System Restore folder. As a result, System Restore has the potential of restoring an infected file on your computer, even after you have cleaned the infected files from all the other locations.

Also, a virus scan may detect a threat in the System Restore folder even though you have removed the threat.

For instructions on how to turn off System Restore, read your Windows documentation, or one of the following articles:
Note: When you are completely finished with the removal procedure and are satisfied that the threat has been removed, re-enable System Restore by following the instructions in the aforementioned documents.

For additional information, and an alternative to disabling Windows Me System Restore, see the Microsoft Knowledge Base article, "Antivirus Tools Cannot Clean Infected Files in the _Restore Folder ," Article ID: Q263455.

2. To restart the computer in Safe mode or VGA mode
Shut down the computer and turn off the power. Wait for at least 30 seconds, and then restart the computer in Safe mode or VGA mode.
  • For Windows 95, 98, Me, 2000, or XP users, restart the computer in Safe mode. For instructions, read the document, "How to start the computer in Safe Mode."
  • For Windows NT 4 users, restart the computer in VGA mode.


3. To restore the Windows Hosts file

Note: The location of the Hosts file may vary, and some computers may not have this file. For example, if the file exists in Windows 98, it will usually be in C:\Windows; and it is located in the C:\WINNT\system32\drivers\etc folder in Windows 2000. There may also be multiple copies of this file in different locations.

Follow the instructions for your operating system:
  • Windows 95/98/Me/NT/2000
    1. Click Start, point to Find or Search, and then click Files or Folders.
    2. Make sure that "Look in" is set to (C:) and that "Include subfolders" is checked.
    3. In the "Named" or "Search for..." box, type:

      hosts

    4. Click Find Now or Search Now.
    5. For each one that you find, note its location. (This is displayed in the "In Folder" column.)
    6. Right-click each file, and then click "Open With."
    7. Deselect the "Always use this program to open this program" check box.
    8. Scroll through the list of programs and double-click Notepad.
    9. When the file opens, delete all the entries in the Hosts file, except for the following line:

      127.0.0.1     localhost

    10. Close Notepad and save your changes when prompted.

  • Windows XP
    1. Click Start, and then click Search.
    2. Click All files and folders.
    3. In the "All or part of the file name" box, type:

      hosts

    4. Verify that "Look in" is set to "Local Hard Drives" or to (C:).
    5. Click "More advanced options."
    6. Check "Search system folders."
    7. Check "Search subfolders."
    8. Click Search.
    9. Click Find Now or Search Now.
    10. For each one that you find, note its location. (This is displayed in the "In Folder" column.)
    11. Right-click each file, and then click "Open With."
    12. Deselect the "Always use this program to open this program" check box.
    13. Scroll through the list of programs and double-click Notepad.
    14. When the file opens, delete all the entries in the Hosts file except for the following line:

      127.0.0.1     localhost

    15. Close Notepad and save your changes when prompted.


4. To reverse the changes made to the registry


WARNING: Symantec strongly recommends that you back up the registry before making any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified keys only. Read the document, "How to make a backup of the Windows registry ," for instructions.
  1. Click Start, and then click Run. (The Run dialog box appears.)
  2. Type regedit

    Then click OK. (The Registry Editor opens.)

  3. Navigate to the key:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

  4. In the right pane, delete the value:

    "NetLink"="netlink32.exe"

  5. Do one of the following:
    • Windows NT/2000/XP. Skip to step h.
    • Windows 95/98/Me. Proceed with step f.

  6. Navigate to the key:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\
    RunServices

  7. In the right pane, delete the value:

    "NetLink"="netlink32.exe"

  8. Exit the Registry Editor.

  9. Restart the computer in Normal mode. For instructions, read the section on returning to Normal mode in the document, "How to start the computer in Safe Mode."


5. To update the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:
  • Running LiveUpdate, which is the easiest way to obtain virus definitions: These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate).
  • Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater).

    The Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.

6. To scan for and delete the infected files
  1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
  2. Run a full system scan.
  3. If any files are detected as infected with W32.Gaobot.WO, click Delete.


Writeup By: Hiroshi Shinotsuka