Chet Wisniewski, a security researcher with U.K.-based Sophos, confirmed that the update alerts users when they try to download any of the bogus MacDefender antivirus software.

Wisniewski had not yet tested the malware cleaning functionality of the update, but was confident that it would work.

"It's reasonably trivial to remove MacDefender," said Wisniewski, using the name for a growing family of scareware. "It's not burying itself in the system, not compared to some of some of the crap that we see on Windows."

Tuesday's update, labeled , adds a new definition to the embedded in Mac OS X 10.6, aka Snow Leopard, and also increases the frequency with which the operating system checks for new definitions to daily.

Before today, Apple had added only five detection signatures to the antivirus component of Snow Leopard.