I m dealing a huge LAN/ISP with 400 users . the problem is that there is a chinese virus which continuously attacks different computers on the LAN . It creates an IP conflict because it makes the infected computer as the Gateway for internet and all the computers stop accessing the internet . No antivirus can catch it coz i have tried every version of it.There is no way but to format the computer and and then connect with the internet. My servers are based on Linux , less those all r continuously effected and my ISP is losing Repute because of frequent formating of the computers. If anyone has got any way out please tell. me

what are you using for a firewall between you and the internet? Does it support software subscriptions like Antivirus filtering? Your being infected has nothing to do with your ISP. You can not blame them. Sounds to me that you don't have a virus but malicious code has been installed in your location. It is replicating itself. It does not have a signature like a virus does so it can not be detected by AV.

There was a government branch that had been infected. (big name AV company)was called in to help fix it. After a few days they stated that it would be impossible to fix the department. The only sure was was to clean install every computer. We are talking about a few thousand. If you can't contain it you have to stop all operations. Consider live linux cd's for temp access. Consider pxe load of all systems at one shot. I would never allow any ISP access to company computers. You should attempt to either get hardened and harder systems and separate your lan from the net. "Best Practices", Event viewer, host file, perfmon, antivirus, anti-spyware, Live CD's, backups, are in my top 10