In what appears to be a first, Apple is recommending that Mac users install antivirus software.

But don’t read this as an admission that the Mac operating system is suddenly insecure. It’s more a recognition that Mac users are vulnerable to Web application exploits, which have replaced operating system vulnerabilities as the bigger threat to computer users.

Apple quietly signaled its shift with an item titled “Mac OS: Antivirus utilities” posted on its Support Web site November 21: “Apple encourages the widespread use of multiple antivirus utilities so that virus programmers have more than one application to circumvent, thus making the whole virus writing process more difficult.”

The item offers three software suggestions: Intego VirusBarrier X5 and Symantec Norton Anti-Virus 11 for Macintosh, both available from the Apple Online Store, and McAfee VirusScan for Mac.