From Network Associates
Virus definition, or .DAT, files contain up-to-date virus signatures and other information that Network Associates anti-virus products use to protect your computer against the thousands of computer viruses in circulation. Whether it is VirusScan, VirusScan Pro or Internet Security Suite, make sure you have the very latest Internet protection.
Network Associates releases new .DAT files regularly to provide protection against the approximately 300 new viruses that appear each month
McAfee Updates, released for December 11, 2012