On March 18, along with the latest version of iTunes and QuickTime, Apple slipped a copy of Safari 3.1 into the Software Update it sent to millions of Windows users — even though strictly speaking the first non-beta version of Safari for Windows was a new program and not an “update.”

Critics, among them longtime Apple supporters, excoriated the company for what was widely viewed as an uncharacteristic sleight of hand. They called it “disgraceful,” “malware” and a violation of the “trust relationship great companies have with their customers.” (See for example here)

What they didn’t call it was effective. But data released on Thursday by Net Applications show that the brief experiment worked rather well. During the month that it lasted, the percentage of Safari for Windows users among Net Applications’ clients, which had never climbed above .07%, grew three-fold, to .21%.

It might also have helped that the program was getting good reviews, although it’s not clear how many Microsoft (MSFT) Windows users would ever have tried Apple’s (AAPL) Web browser if it hadn’t been shoved in their face.

On April 18, Apple revised its Software Update protocol. New programs are now clearly marked as such and the box to accept them is unchecked by default.