Watch Paint Dry is “a sports-puzzle game that evolves around one mysterious cutscene. Bringing in innovative gameplay and requiring high attention to detail, Watch Paint Dry is a must play for anyone who enjoys mystery ARG type games.” Or perhaps I should say, it was: It appeared on Steam over the weekend, but only briefly—because it wasn't supposed to be there at all.
If you think it sounds like a gag, there's good reason: That's precisely what it was. The whole thing was cooked up by UK-based security researcher Ruby Nealon, who was inspired to pull the prank after efforts to report a loophole that allowed games to be put on Steam without Valve approving them went ignored.
The process for getting the “game” on Steam, which he posted on Medium, is fairly complicated, but also obviously not nearly as complicated as it should be. The big dependency is having access to Steamworks, Valve's internal publishing platform.
Using the ID number assigned to his app didn't work, but tying it into “sessionid” he dug up while getting the Steam trading cards approved (a process he explains earlier in the post) made the magic happen.
“I will admit that it appearing straight away in the new releases section was an oversight on my part. I initially wanted it to have 'Coming April 1st' and not show up until Friday (though I wouldn’t have expected it to last that long),” he wrote. “I will also admit I was very tempted to try and see how far along releasing it I could get, but I think it’s for the best that the app is not listed for sale.”
Nealon has since been in contact with Valve, and the loophole has been closed, which is presumably why he felt safe making the process public. He said his escapade has taught him a few things about working with user-generated content (foremost among them presumably being, “don't allow users to set the item to 'Released'”), and he apparently suffered no consequences for it. That's a happier outcome than the one that met Euro Truck Simulator 2 developer Tomas Duda when he exposed a different Steam vulnerability with an amusing prank of his own a couple of years ago: He ended up with a one-year ban from Steam for his troubles, although it was fairly quickly overturned once the word got out.
Watch Paint Dry is no longer available on Steam, but you can still play around with it thanks to the magic of Google cache.