Is there a World of Warcraft server that is virus free

Please note: The information contained within this answer may be illegal and against Blizzard's Terms of Service. USE AT YOUR OWN RISK!

The official servers that are managed by Blizzard are all virus free. Since these are the official servers, you do not need to worry about any personal information ending up in the wrong hands. On private servers, you do need to worry to a certain extent.

Most private servers are free to play and provide an in-game experience that may differ totally from the official game. The GMs (Game Masters) on these servers are inexperienced and may use deceptive techniques to gain information from you, or to take control of your computer. Also, the account creation forms are often insecure, allowing third-parties to intercept your information.

In all honesty, private servers should not be used under any circumstance. I do believe the client holds a cache of servers you were on, and if a Blizzard GM discovers you were using an unofficial server at some point, he/she could ban your account and Blizzard could hold you liable for infringement.

I have included a link to Blizzard's Terms of Service. Pay close attention to Section 2, articles E to G.