The Advertising Standards Authority has banned a Dungeon Keeper advert it ruled had misled customers.

A direct email for the controversial mobile game drew a complaint from one user who "challenged whether the ad was misleading because it omitted significant information", the ASA said. After an investigation, the ASA found the ad breached its code, and today published its ruling.

Dungeon Keeper was heavily criticised upon its release for its heavy-handed in-app purchases. Eurogamer's Dungeon Keeper review dug up a 1/10. At E3 last month EA boss Andrew Wilson admitted the company had "misjudged" the game's economy and described the project as a "shame", before promising to learn from the experience with future free-to-play titles.

The Dungeon Keeper ad in question stated:

"GET DUNGEON KEEPER ON MOBILE FOR FREE! ... DIG. DEVISE. DOMINATE. Build the most badass dungeon ever! Raise an army of diabolical minions and lay twisted traps to destroy any opponents foolish enough to set foot in your lair. MASTER THE HAND OF EVIL Cast powerful spells, pillage and plunder other players' dungeons, and slap your imps around to make them work harder. A world of wicked fun is right at your fingertips. What are you waiting for, Keeper? Get it for FREE!"

The ad also included a screenshot of the game which appeared to show a well-developed dungeon, and was accompanied by artwork depicting characters from the game.

The complainant understood that gameplay was severely limited unless in-app purchases were made, the ASA said.

Dungeon Keeper launched earlier this year and was heavily criticised by fans of the Bullfrog original.

EA's UK branch, based in Guildford, and the ASA had a back and forth over the issue. EA, as you'd expect, responded by saying it had not misled or omitted information from the ad, and insisted that "in-game content is available to all players, whether or not they make in-app purchases", and that "gameplay without in-app purchasing is not severely limited".

Dungeon Keeper's in-game currency cropped up in the response. The game uses two grind currencies: stone and gold, which you get by playing the game. There's also a premium currency called gems, which most free-to-play mobile games use. You can buy these with real money or earn them in the game.

EA said that because players can earn gems by digging out dungeon areas, winning achievements and timed event raids, it was possible for a player to accrue all three currencies for free over time just through normal gameplay.

Of course, if you want to speed up the process you can buy gems, but EA said because gems were regularly awarded through interaction with the game it was possible to unlock the same content through gameplay.

The issue was whether this was made clear by the ad. EA said all the content and activities identified in the ad could be achieved by players who play for free. It pointed out that the in-app purchases are stated in the product description for the game, and then explained in the tutorial and the purchase process for the gems.

EA even provided data for the game that apparently showed that non-spenders were well represented in the number of players who reached the middle and end of the game - and that non-spenders did not reach these points "substantially slower" than spenders.

"They stated that the average player would expect a free-to-play title to be monetised with countdown timers and premium currency, and mentioned popular titles that use this feature," the ASA said.

"They stated their belief that the mechanics of Dungeon Keeper were well within the average length and frequency for the market and that players of combat simulators would therefore reasonably expect them. Electronic Arts also stated that the timers and premium currency did not only function as a monetisation strategy, but balanced gameplay and provided players with a sense of progression and enabled resource management. They said that even if there was no monetisation in the game a timing mechanism would still be present."

So, with all that said, why did the ASA uphold the complaint and ban the ad? Well, according to its ruling, it seems the watchdog was pretty clued up on how Dungeon Keeper - and free-to-play mobile games in general - work.

"We understood that several mechanisms within the game took a significant amount of time to be completed, and that these would only be speeded up by using the premium gem currency," the ASA said.

"We noted that, although some of these actions could be done simultaneously, there was a limit to how many actions could happen at the same time and that the length of the countdown timers increased according to how far the player had progressed in aspects of the game.

"We therefore regarded it as extremely likely that players would reach a position where they would be unable to take any further meaningful or progressive action in the game until a timer had finished or been skipped, and that these periods would become longer and more significant, and the cost of skipping increasingly higher, as the player progressed."

The ASA also spotted that some of the features mentioned by the ad that did not require waiting for a timer were "either incidental or brief" - including slapping the imp characters.

"From the information available in the ad, players would expect the gameplay progression and their ability to advance to be unhindered by unexpected and excessively onerous delays, and we therefore considered that the length and frequency of these countdown events was beyond that which would be reasonably expected by players," the ASA declared.

"We consequently considered it likely that many players would regard the gameplay experience as unexpectedly curtailed and as a result would need to spend gems in order to achieve the form of gameplay anticipated."

Speaking of Dungeon Keeper's gems, the ASA said the rate at which they can be gained was slow compared to the amount needed to play the game at a reasonable rate.

"Given this, we considered that players were likely to find themselves in a situation where they wished to bypass timers to achieve the expected gameplay as above, but were unable to do so without making a monetary purchase of the Gem currency."

The ad, the ASA said, should have made clear what consumers could expect from Dungeon Keeper's free elements and that in-app purchases would have a significant impact on gameplay. The ad, the ASA noted, did not include any reference to in-app purchases or mention the role they would play in the game.

"While we understood that the average consumer would appreciate that free-to-play games were likely to contain monetisation functions, we considered that they would also expect the play experience of a game described as 'free' to not be excessively restricted.

"Similarly, although we acknowledged that a timer mechanism could be a legitimate part of gameplay experience, the nature of the timer frequency and length in Dungeon Keeper, in combination with the way it was monetised, was likely to create a game experience for non-spenders that did not reflect their reasonable expectations from the content of the ad.

"Because the game had the potential to restrict gameplay beyond that which would be expected by consumers and the ad did not make this aspect of the role of in-app purchasing clear, we concluded that it was misleading."

The upshot of the ruling is that the ad must not appear again in its current form.

The final word goes to the ASA: "We told Electronic Arts Ltd to ensure that future ads made clear the limitations of free gameplay and role of in-app purchasing with regard to speeding up gameplay."

It looks like the ASA ruling is an example of it applying the UK's Office of Fair Trading's 'Principles for online and app-based games' it set out following an investigation into exploitative micro-transactions.

Back in January the OFT said in-game payments should not be authorised without the express permission of the account holder, and if there were any hidden costs associated with the game, they must be stated upfront. In-game advertising must be declared, as must any use of personal data.