Apple has unleashed an all-new 'Get a Mac' ad, and this one hits Windows where it's weakest — security.

The US ad debuted yesterday and is being broadcast on US TV as well as online.

In a sketch clearly aimed at exposing just one of the weak spots in Windows Vista, Apple's ad is critical of Microsoft's intrusive User Account Control (UAC) element, and of Windows security across the board.

The ad features a third character who represents the UAC. The third character interrupts the flow of communication between Mac and PC with a constant string of permission requests.

The ad follows Microsoft chairman Bill Gates' statements last week in which he claimed Macs are broken into by malicious users "every day", when speaking to Newsweek.

You'll find the new ad here.