Microsoft said Wednesday that a buggy antivirus definition update, released Friday, had mislabeled Skype as pop-up adware program called Win32/Vundo.gen!D. The issue was fixed Monday in a signature update so users who have version 1.31.9121.0 of Microsoft's malware signature file should be fine.
Microsoft's security products were not removing Skype, simply blocking it from running, so users should not have to install any new software once they've updated their antivirus definitions. "Once the signatures are updated on the user's machine, Skype will operate normally," Microsoft's public relations agency said in a statement.
The buggy update affects Forefront Client Security, Windows Live OneCare and Windows Live OneCare Safety Scanner, but not Windows Defender or the Malicious Software Removal Tool that ships with Windows.
Microsoft's gaffe was an annoyance for users, but security products often mistakenly report legitimate software as malware, called a "false positive," by security experts. Two years ago, for example, Sophos identified legitimate Mac OS X files as malware.
Skype has blogged about the issue here.
The latest signature files can be downloaded here.