Further complicating the situation was a tussle last fall over a new security management console for Vista that security vendors complained would affect the performance of their products. Microsoft eventually agreed to release application programming interfaces that enable other vendors to disable the built-in console.

In addition, security vendors say that porting their products to a new operating system is inherently more time-consuming than moving over other applications is.

"You have to be more careful than with a productivity app," said John Dasher, director of product management at encryption tools vendor PGP Corp. "If something goes awry, people can lose data."

Palo Alto, Calif.-based PGP is blocking its users from even installing non-Vista-ready versions of its software on the new OS. The company released a Vista-compatible beta of its PGP Desktop 9.6 software two weeks ago, but Dasher declined to predict when the final version would be ready.

All of the factors facing security vendors are adding up to more development work for companies such as Check Point Software Technologies Ltd., maker of the popular ZoneAlarm firewall.