Acclaim's first game to feature in-game ads will be BOTS, a free MMO with an action theme. BOTS is currently one of the most popular MMOs in Asia, and is being redesigned for its release in North America and Europe.

"We are focused on providing the best online multiplayer games for free, something rare in the market. In order to do this, we are using innovative business models including adding in-game advertising, selling in-game content and offering unique subscriptions. Massive has the most established and robust in-game advertising solution, with deep experience in multiplayer games, and so were the natural choice as our partner," said Howard Marks, CEO of Acclaim.

"Acclaim is a great addition to the Massive Network and we're thrilled to work with them to integrate real-world ad campaigns into their games," said Nicholas Longano, President of New Media at Massive. "This partnership further emphasises the growing support for the realism and revenue benefits that dynamic in-game advertising provides. This is a tremendous win for gamers - free games supported by advertising."

Massive's roster of clients now includes more than 36 publishers and developers, covering over 100 games. While in-game advertising is a topic of much debate at the moment, it's hard to argue about it in a MMO that requires no monthly fee.