Half-Life 2 launches at retail - and online

One of the most eagerly awaited PC games in history, Half-Life 2, has launched at retail outlets around the world today - and has simultaneously been made available on the systems of those who purchased it directly from developer Valve over the Steam distribution system.

The game, which is expected to be the biggest title on the PC this year, is one of the first ever to be distributed in this manner - and indeed, the Steam system has proved a bone of contention between Valve and publisher Vivendi.

At present it's not known how many purchases have been made over the Steam system, but if the numbers add up to a significant portion of overall sales, the launch will undoubtedly be presented as a strong proof of concept for online content distribution.

Half-Life 2 is a product which has been no stranger to controversy; aside from the disagreements with Vivendi over Steam, which have spilled over into an unresolved legal battle between publisher and developer, the game also made headlines when its source code was stolen by hackers, and subsequently when it was repeatedly delayed from its originally announced September 2003 release date.