Glu has removed the adverts from its iPhone game Space Monkey and reverted it back from free to a paid-for title, after complaints from consumers who'd paid for it previously.

The game only went ad-funded last week, when Glu dropped the price to free and included adverts in between levels, courtesy of mobile advertising network AdMob.

The problem appears to be that people who'd paid for the game also got the ads after the game was updated. Several posted negative 1-star reviews on the App Store to complain.

Samples? "I'm absolutely disgusted, I paid for this app! Now I have to suffer ads which should have been released as a separate version..."

And also: "I paid for this app! Why should I see ads? Create a lite version if you want to show ads!"

To its credit, Glu has reacted quickly and reverted the game to its most recent price of £0.59, without ads. The publisher has apologised on the game's App Store page too:

"We have heard your feedback loud and clear and we sincerely apologize for causing you any distress over the in-game ads in Space Monkey. When the monkey started screaming and throwing junk at us, we knew we had to get the cosmos back in order. For our existing customers who have previously bought the game or tried the free version, we have removed the ads and updated Space Monkey with all the new features."

It's a valuable lesson both for Glu and rival developers and publishers, as many will be tempted to use ads as a way to squeeze more revenue out of games as they reach the end of their natural sales lives on the App Store.

It raises the prospect of three separate versions of an iPhone game being available: a premium version that's paid for, a free 'Lite' limited demo, and then later in its lifespan, an ad-funded free full version.

Meanwhile, the whole affair shows one of the key strengths of the App Store, which is players' ability to express their anger through the ratings process.