"We believe strongly that when you buy a game from us, you shouldn't be forced to install and run a 3rd party software client to be able to play the game you purchased," D2D explains in a statement masquerading as a listing for Modern Warfare 2 in its store. A representative later told Kotaku "We don't believe games should force the user to install a Trojan Horse."

Modern Warfare 2 on PC will use Steam and Valve's Steamworks framework for DRM purposes as well auto-update, achievement and anti-cheat features, among others.

However, both Direct2Drive and GamersGate sell ACE Team's Zeno Clash--which requires Steam. D2D also offers several other Steam-based titles, including Empire: Total War and Warhammer 40,000: Dawn of War 2.

"We share some of the same concerns as Direct2Drive over the bundling of the Steam client with the game," Impulse told Voodoo Extreme. "The most obvious issue is the forced inclusion of a competitor's store that blocks us from carrying the game."

This latest Modern Warfare 2 upset comes hot on the heels of controversies over a terrorist sequence and the fact that the PC version will not support dedicated servers.

Call of Duty: Modern Warfare 2 is expected to be one of the biggest titles of the year when it arrives for PC, Xbox 360 and PlayStation 3 on November 10, with retailer GameStop reporting that pre-orders are "the highest for any title we've ever sold."