Publisher Slashkey has put up a post on their official forums warning users about the malicious ads. "If you suddenly get a warning that your computer is infected with viruses and you MUST run this scan now, DO NOT CLICK ON THE LINK, CLOSE THE WINDOW IMMEDIATELY. You should then run a full scan with your antivirus program to ensure that any stray parts of this malware are caught and quarantined." Hundreds of users have posted to the forum reporting problems playing the game or seeing the fake virus ad.
While Slashkey writes that they "believe at this time that [the spyware is] harmless to your computer," security firm Sophos recommends users "stop playing the game ...until the makers of Farm Town resolve the problem of malicious adverts." More as it develops.