14 DAY TRIAL // Earlier today, Avira users were unable to access Google, CNN and other popular websites, because of bogus detections triggered by the WebGuard component.
"For a short time this morning (between 7:00 am and 8:45 am MEST), some domains slipped through into our WebGuard filtering system which caused some users to not be able to visit some regular web sites," the German antivirus vendor announced on its blog.
Avira is one of the biggest providers of anti-malware products in the world. Earlier this year the company claimed a user base of 145 million.
However, it's worth pointing out that the free Avira AntiVir Personal, accounts for a vast majority of those users and this product doesn't have the WebGuard component.
According to reports on the company's support forum, when trying to access several popular websites, users received an error reading:
"In order not to compromise your security, this page will not be accessed. The requested URL was identified as a potentially harmful website."
Apparently, the links were improperly detected as phishing URLs by new filters introduced as a result of a recent spam campaign, which employed some special techniques.
The junk emails in question, which we reported about on Tuesday, used HTML-based tricks to advertise rogue online pharmacies.
They also included hidden links for several major websites like Google, Yahoo!, Amazon or AOL, in an attempt to evade spam filters.
There is probably an automated mechanism that adds URLs seen in spam emails to the WebGuard filter and unfortunately, in this case, those URLs were legit.
"We are taking precautions so this can’t happen again," the company said. "Our sincere apologies for those who were affected!" it added.
False positive incidents are common in the antivirus industry, however, their impact can vary widely depending on what is being blocked and for how long.
There were cases when businesses suffered as a result or when thousands of computers were no longer able to boot because critical Windows files were wrongfully deleted.