Valve has issued a warning about Steam Early Access, saying developers may never finish their games.

In an update on the Steam Early Access FAQ, Valve asked the question, "When will these games release?", and answered by saying players should be aware that some developers will be unable to finish their game - for whatever reason.

So, only buy an Early Access game if you're excited about playing it in its current state, Valve warned.

"It's up to the developer to determine when they are ready to 'release'," Valve said. "Some developers have a concrete deadline in mind, while others will get a better sense as the development of the game progresses. You should be aware that some teams will be unable to 'finish' their game. So you should only buy an Early Access game if you are excited about playing it in its current state."

The news comes following a raft of high profile cases in which players have complained about the poor quality of Steam Early Access games, and in some cases, the lack of updates post-launch.

Last month Valve hauled first-person sci-fi post-apocalyptic open-world game Earth: Year 2066 from Steam Early Access and offered refunds to disgruntled customers after the game had been labelled "broken" and unfit for sale.

The developer, Killing Day Studios, had also been accused of misleading customers with inaccurate claims on the game's Steam product page.

In 2012 Hammerpoint Interactive's zombie themed MMO The War Z was removed from sale on Steam after the developer was accused of lying on the game's Steam page.

Then, in June 2013, The War Z changed its name to Infestation: Survivor Stories following a trademark issue, reportedly to do with Brad Pitt's film World War Z film.

Valve has come under fire in recent months for the Steam Early Access program, which some say is being abused by developers.

While Early Access, which is designed to let developers sell games before they're finished in order to gain feedback and make improvements ahead of a full launch, has seen huge successes, such as DayZ, Rust and Starbound, it's also seen its fair share of controversy.

In a recent interview inXile Entertainment boss Brian Fargo, currently working on Steam Early Access title Wasteland 2, told Eurogamer he believed Early Access would become more refined as customers become more selective.

"Wherever there is a system there will always be people who push the envelope on what it was set up to do to begin with," Fargo admitted.

The refinement Fargo hopes to see with Early Access titles has to do with what he calls "another class of products".

"They only put up a very little thing hoping to get the money, and if they don't get enough money then they can't finish the game," he said.

"That puts it into a different category and that gets very scary. If you buy Wasteland 2 Early Access you're going to get the game. We're going to finish it. That might not always be the case with everyone.

"So I expect that, again like Kickstarter, that people are going to further refine and scrutinise what it is they're willing to spend money on early on."

Valve has said Early Access is "the way games should be made".

"We like to think of games and game development as services that grow and evolve with the involvement of customers and the community," Valve says of the service.

"There have been a number of prominent titles that have embraced this model of development recently and found a lot of value in the process. We like to support and encourage developers who want to ship early, involve customers, and build lasting relationships that help everyone make better games."