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. Network Associates releases new .DAT files regularly to provide protection against the approximately 300 new viruses that appear each month. To ensure that your anti-virus software can protect your system or network against the latest virus threats, download and install the latest .DAT files.