Hello Bl4ckDi4mond,
Sorry to get to your post so late. If you were banned from Modern Warfare 3, it would be due to violating the Online Code of Conduct that is listed here
http://community.callofduty.com/message/205673932#205673932
Unfortunately, all bans are final and cannot be reversed as all bans are thoroughly checked and verified by the Security team to ensure there are no false positives.
To gcbrothers;
VAC bans are handled exclusively by the Valve corporation and still cannot be reversed. To answer your question; No, a virus cannot cause a false positive as all VAC related bans are thorougly verified by the Valve security team. Please see this Steam support article
https://support.steampowered.com/kb_article.php?ref=7849-Radz-6869
Best regards,
^AxelSpoons