Discovered: December 30, 1999
Updated: February 13, 2007 11:33:11 AM
Also Known As: Win32/Crypto
Type: Virus

W32.Crypto is not known to be in the wild yet. The payload for this virus is similar to the One_Half virus. This means the Crypto virus will encrypt the data on your hard drive, and if you remove the virus, the data will be inaccessible - and effectively held hostage. Crypto uses strong cryptographic algorithms to encrypt the data on the hard disk, making recovery unlikely without a backup.

W32.Crypto uses the Microsoft Crypto API to encrypt accessed DLLs on the system with an encryption key that is added by the virus to the infected system, and installed in the registry as:


The virus first infects the operating system file KERNEL32.DLL. Once infected, KERNEL32.DLL controls all access to other DLLs on the system and the virus encrypts all such accessed DLL files. While the virus is active in memory, it will automatically decrypt encrypted DLL files so they can be used. However, if the virus is not active in memory, the DLLs will not be decrypted and the system will fail to work. Unless the virus is active and running, all DLL files that have been encrypted will be inaccessible. This means that an infected system can only be cleaned by restoring all affected DLL files from backup copies, and deleting all infected executable files. Data files are not encrypted by this release of the virus.

Antivirus Protection Dates

  • Initial Rapid Release version December 15, 2000
  • Latest Rapid Release version February 07, 2017 revision 019
  • Initial Daily Certified version December 15, 2000 revision 041
  • Latest Daily Certified version February 08, 2017 revision 001

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

Writeup By: Peter Szor

Discovered: December 30, 1999
Updated: February 13, 2007 11:33:11 AM
Also Known As: Win32/Crypto
Type: Virus

The virus infects PE (Windows Portable Executable) files by appending itself to the last section of the executable in encrypted form. The virus uses a complex polymorphic engine, meaning that the virus is self-mutating and difficult to detect. The size of the pure virus body is about 20 kilobytes, thus W32.Crypto is a very large virus.
During test infections, the virus failed to infect most systems and on others it infected a few files causing Windows to stop working. However in a few Windows installations, the virus does appear to work correctly.
When an infected file is executed, the virus infects KERNEL32.DLL in the \Windows directory. It is interesting to note that the virus is not encrypted in the KERNEL32.DLL file, and its logic can be seen with any common viewing tools.
Infected KERNEL32.DLL files will contain a lot of visible strings including: Win32.Crypto, (c)oded by Prizzy/29A Greetz to Darkman, Benny and GriYo Kiss Of Death
In order to cause the infected KERNEL32 file to be used by the Windows operating system, the virus creates a wininit.ini file. This wininit.ini file instructs Windows to use the infected KERNEL32.DLL file the next time the machine is rebooted.
When the KERNEL32.DLL is infected, it will call the virus code as files are accessed on the system. The virus attempts to infect 20 files during boot time and also checks for known archive files and infects them by using the available archives on the machine such as: PKZIP.EXE, ARJ.EXE, RAR.EXE and ACE.EXE. The virus adds infected files to the archives it locates.
Crypto is a retro virus. It pays attention to certain software debuggers. It deletes anti-virus data files and also disables some active anti-virus protection.
The virus targets the following anti-virus files:


W32.Crypto does not infect popular anti-virus software or some other common applications that have self-check routines. It will refrain from infecting programs with names beginning with:
  • TB
  • F-
  • AW
  • AV
  • NAV
  • PAV
  • RAV
  • NVC
  • FPR
  • DSS
  • IBM
  • INOC
  • ANTI
  • SCN
  • VSAF
  • VSWP
  • FSAV

The virus also avoids infecting specific system executable files that are monitored by the operating system for changes. Such protection is available in Windows 2000 and Windows 98SE.


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: Peter Szor