An update to Network Associates' McAfee VirusScan anti-virus software has been found to damage the master boot record of Windows NT 4.0 computers, forcing customers to reinstall their operating systems.

The problem occurred because of a conflict between VirusScan/Netshield 4.0.2 - which is now two years old - and the 4120/4110 SuperDAT utility, which automatically updates antivirus protection with a file that contains the latest signature profiles.

In a statement Network Associates said it had pulled the suspect virus definition (or .DAT) libraries and reposted files which do not cause the conflict. It also said that even if the MBR is damaged programs and data on the hard disk should be safe, so reinstalling the operating system will restore the MBR.

"The incompatibility was with a product that was over two years old. It's imperative that people update not only their engine and dats, but also the product itself regularly as new versions are released to ensure up-to-date protection from malicious code," the statement said.

Network Associates builds its virus detection software from three component technologies: a product executable, the scan engine and the virus definition libraries, which contain signatures of the latest viruses. The SuperDAT utility updates the scan engine and virus definition libraries.

The latest version of the VirusScan/NetShield program executable is 4.5 and users are recommended to upgrade to that.

Only last month a similar conflict occurred between another older scan engine and a virus definition file. This raises the interesting question of why Network Associates allows the latest virus updates work with older versions of its scanning engine - but unfortunately no-one from Network Associates was available to field this question.

Conflicts are inevitable, and can be expected again, because the update utility makes assumptions about the functions available in the executable. Other vendors make the latest virus definition files incompatible with older scanning engines and it would make a lot of sense for Network Associates to adopt this approach. ®