The developers of Lugaru HD, a game available for $9.99 (about £6.30) in the Mac App Store, has cried foul over what it claims is a "counterfeit" version of the game also available in the Mac App Store at a hefty discount.

The source code of Lugaru HD was opened up to the public in the hope of giving "more opportunities for modders and novice programmers to experiment with full game engines" but Wolfire Games, the original developer, is presumably cursing its community-minded gesture after discovering the 'fake'.

"You can imagine our surprise when we saw it listed on the Mac store for only $0.99! When we looked into it further, we saw that it was uploaded and sold by someone we had never heard of and had the name 'Lugaru' instead of our 'Lugaru HD'," Wolfire Games wrote on its blog.

The Kotaku website reports that the people behind the other version of Lugaru, iCoder, claimed to have every right to sell the game as Wolfire Games made the source code available to everyone in a blog post in May last year.

"While we do understand Wolfire's regrets, this does not change the fact that we have every legal right to market and sell the software, and we feel that $1.99 is a fair price," Alex Matlin of development team iCoder told Kotaku. Oddly, Matlin doesn't mention whether he thinks that 99c - what iCoder's version of Lugaru is actually selling for - is a fair price.

But Wolfire was adamant that it had not released the rights for other developers to sell Lugaru as their own. "Open-source software is not freeware. It's as legal for them to sell Lugaru as it would be for them to sell Quake 3, Marathon, Aquaria, or Arx Fatalis. That is to say, it is completely illegal."

"Ignoring the fact that this is obviously a violation of our license, the reason we made the source code available is to give more opportunities for modders and novice programmers to experiment with full game engines and help promote the message of the Humble Bundle. Corrupting this effort for fraudulent financial gain is the worst ethical violation we've ever experienced," the blog post continued.

The majority of comments on the Wolfire Games' blog seemed to support the original developers. "It's sad that this has happened to a company which has been at the forefront of championing open and open-source development. It's a real spit in the eye, couldn't have happened to nicer guys," one wrote.

"Not cool - whoever did that should lose a nut," wrote another. Apple said it was looking into the issue but did not provide any further details.