None of us ought to be surprised that some people try to use Steam's rather open marketplace to peddle malicious software, but it would seem that some users have come across one "game" that is so bold in packing malware that it's almost impressive, on some level. The game in question is Abstractism.
This game - vaguely described as 'an absolutely trivial platformer', seems rather innocuous at first. Like one of those faceless, tasteless indies that get slapped together in hopes of getting a sale or two every once in a while. Abstractism, however, is rather more malicious than it might seem at first.
One of the users purchased the game and set it up on a virtual machine, and then reported a very, very significant resource consumption that does not correlate with the game's graphical quality or complexity and a CPU/GPU/RAM usage that is consistent with that of an average crypto mining tool.
The resources in question also include a "sizeable amount of disk space which again is not expected from a game of this complexity; but is expected of a crypto miner." There is also a huge spike of network activity once Abstractism is launched, and the port usage coincides with that of a particular type of miner.
Furthermore, there have been reports of developers scamming people via the Steam Marketplace by creating items that look like expensive TF2 cosmetics, and they've been found to peddle politically-charged, anti-semitic stuff. Almost comically evil, right? In any case, best steer clear of Abstractism, and keep track of resource usage on your PC in general.