Instant messengers and virus question...

[Hypo_Luxa]

A little background first. I built a system for a close friend a while back and at first everything was fine. About 6 months ago, he got a warning from NAV that he was infected with an IRC trojan. NAV was unable to remove the infection so I recommended we do a clean install just to be sure. I went so far as to do a low level format on the hard disk, repartition, format and clean Win2K install. I installed all his apps myself, from known clean source disks. I set him up with NAV again as well as Zonealarm. (is on cablemodem) All was well for about a month, then he got reinfected with the same virus. He claims not to have downloaded any new software or files except for a few MP3s which I scanned and were clean. I scanned all his cd-roms and floppies, nothing. I know for a fact all my media are clean. We rereinstalled everything again and he was reinfected within a week. The only x factor in my eyes is his yahoo messenger. He uses it quite a bit, has probably 30 contacts some of whom he barely knows if at all. He also gets into yahoo chat rooms quite a bit. I am wondering if he is getting infected through his yahoo messenger from one of his contacts? I am not familiar enough with IMs to know how likely this is. I need to figure this out ASAP. Any input is appreciated.

[OS-Wiz]

I doubt IMs are the culprit. ANY download could carry the virus he's getting. You need to determine which download site(s) was common to each occurrence of the virus. Also, go to Symantec's site and see if thay have a special removal tool you can download.

[muisejt]

IMs can be the cause, they have security holes that allow hackers to get into your system with out your knowledge and then they can put a trojan on. if you know where to look you can find programs for doing this