avast! has one of the most popular free antivirus solutions ever and, like any other security vendor, they provide also commercial solutions, with additional goodies included. If you are curios about avast! Internet Security 6.0 and what it offers in exchange for the $39,99 license – check out this comprehensive review.
Security for Everyone – Reviewing avast! Internet Security 6.0
I used Avast for many years. Then recently I turned on my computer and it wouldn’t let me in. Windows claimed that something had tampered with a critical system file and that I would have to verify my ownership of Vista. The solution turned out to be the removal of Avast in the Safe mode through the control panel.
Several other people are encountering the same problem. Avast is not addressing it.
http://social.microsoft.com/Forums/en-US/genuinevista/thread/e2f066b3-2517-41bc-8fad-4c036f2f4ac8