Avast Software has discovered that one multi-user license for its Pro Antivirus was at one point being used by 774,651 individuals in over 200 countries. It started as a 14-user license for a small firm in Tucson, Arizona issued on June 30, 2009 but grew exponentially in use by late 2010. Except for the original 14 users, all of the others were pirates.

The speed at which the pirated license spread from Arizona was accelerated by warez sites, and Avast was quick to point out the "paradox" in computer users looking for "free" antivirus programs at locations with a known reputation for spreading malware. The avast Virus Lab has more than once documented examples of warez sites distributing packages of a "cracked" antivirus programs combined with malware.

The pirated license for the pro version gave a quarter of a million computers access to two additional features: a virtualization sandbox and a script shield. Other than that, the users didn't gain much, given that the same antivirus engine is used in the free and pro versions of avast's antivirus. Nevertheless, the identified users were sent a pop-up (pictured above) notifying them that they had a pirated license and that they would be cut off from virus database updates. They were also given the option of converting to the free version or buying the pro version.

"We made a decision to see just how viral this one license for avast! Pro Antivirus could be. The answer is 'very'," Vince Steckler, CEO of AVAST Software, said in a statement. "Now we are in the process of converting these pirates over to legal products."