Symantec's invention has been at the patent office since 1999 and is the main part of any Symantec product.
The move is seen as a way of seeing off some of its rivals, such as McAfee and the new entrant Microsoft.
It means that Symantec can sue McAfee which offers a similar product, with similar technology.
It has another weapon to use too. In 2003, it spent more than $62.5 million to acquire the Hilgraeve Patent, purported to encompass antivirus scanning.
You can read more at the Herring that is Red.