The projectile was well aimed. The Microsoft boss was reduced to a slapstick figure of fun, his spectacles plastered over and his suit of the finest cloth bespattered with gunk.
Topping the list of potential suspects is Noel Godin, a kind of Belgian Dennis Pennis armed with confectioner's custard, who specialises in leaving egg on the faces of the rich and famous. Previous victims included the French philosopher Bernard-Henri Levy and the film-maker Jean-Luc Godard.
The Microsoft boss, whose personal wealth at Christmas was believed to have topped a prodigious $36.8bn (pounds 23bn), came under fire as he was on his way into the Concert Noble, where he was about to attend a reception hosted by Flemish politicians. Two men were arrested.
A Microsoft spokesman said the company would not be pressing charges for the attack. Gates was unhurt, though visibly embarrassed, and after a clean-up in a side room emerged for a meeting with the Flemish Prime Minister Luc van den Brande.
The custard missile may have been the work of a self-publicist, but there are plenty of other signs that public opinion, not least in the United States, wants to see Gates eat humble pie.
All this in spite of some cringe-making displays of "humanity" on late- night talk shows in the US, where he sang "Twinkle Twinkle Little Star", and a public pledge to outdo CNN's Ted Turner in the philanthropy stakes.
In his worst legal defeat, America's Justice Department recently ordered the Microsoft boss to stop forcing computer manufacturers to install Miscrosft's Internet browser on its PCs. The furore surrounding the case transformed Gates' image - from the charmless but harmless lord of the computer world's geeks and nerds to a bully bent on world domination.
Now there are reports of crossed wires in cyber-wizzard's new $40m palace. "I brought up a big screen in my bedroom to watch a programme and for some reason the system stopped working," he confessed to TV talk-show host Barbara Walters. "It was sitting there shining and I wanted to go to sleep. So finally I had to get a blanket and put it over the screen."Reuse content