Avira has said that it "deeply regrets any difficulties" after a false positive hampered its users this week.
According to a report by The Register, a Microsoft Windows service pack, issued on Monday, caused the Avira ProActiv monitoring software to block operating system processes it believed were infected.
This left users of Avira Professional Security, Avira Internet Security 2012 and Avira Antivirus Premium 2012 with malfunctioning or inoperable systems after iexplore.exe, notepad.exe and regedit.exe were all blocked, along with updates for Microsoft Office and Google Updater.
Avira said "the application blocking issue has been settled in our latest product update" and that the current versions of Avira's Windows desktop products were now operating smoothly. “We deeply regret any difficulties this has caused you. Thank you for your patience and understanding,” it said.
It added that if users continue to encounter the issue, they should update their software, and offered advice on how to disable ProActiv.
Back in 2010, anti-virus vendor Bitdefender flagged some Windows files as Trojans and quarantined them, causing problems for users.