If the virus is getting detected again and again or it is getting re-infected that means.
Either some computer or media is re-infecting this system ( Flash Drive,CD/DVD or some unpatched infected computer)
or there are still some file which is not getting detected as a threat and they are redownloading the worm and is infecting.
have you turned on Autoplay.very first thing to do in case of Worm.
Clear out all temp folder and temp internet content.
If you find any suspicious file submit it
https://submit.symantec.com/basic