Let me tell you a story. It involves an arcade game, the CIA, epilepsy, suicide and one of the greatest urban legends in all of video gaming.
Long before the internet existed as we know it today, and long before more contemporary hoaxes about creepy video games, came the story of Polybius. It existed in many forms, each a little different from the last and each altered slightly to suit the tastes (or memory) of the teller. But all have a few things in common.
The story, as it's told, normally begins in Portland in the early 1980s. It involves crazy lines spurred by feverish word-of-mouth from local arcade gamers. And many of those gamers end up addicted, sick and plagued by nightmares. Some tellers even sprinkle in reports of the game wiping people's memory, or even driving players to commit suicide.
And that's just for starters. The myth of Polybius would have you believe that the game was actually operated by the CIA, or the CIA working with Atari, or a company called Sinneslöschen, which may have been German or may have been the US government. Apparently "men in black" would collect data from the machines from time to time, gathered not just from player's performance but from the subliminal messages that would flash on the screen (and were supposedly the cause of many of the deadly side effects).
Bananas, right? Yet that's the beauty of it, and the reason it grew into such a fanciful tale. While it's easy to assume it's bullshit, there's been no way to prove it never existed. And so the tale has lived on, and even today, there are those who believe that, in some form or another, the game actually existed, and actually made people sick.
One such tale, and if there's to be any truth to the matter this must surely be ground zero of the whole mess, is that the Polybius myth originated from location testing for arcade classic Tempest. The urban legend has Polybius as playing very similarly to Atari's 1980 shooter, so it's possible, however remotely, that it was a faulty Tempest cabinet - one perhaps inducing photosensitive seizures - that's the grain of truth at the heart of this grand, decades-old lie.
While everything you read about Polybius will be tainted by the tale and the nature of the legend (even the game's Wikipedia entry is a minefield), this 2007 write-up is probably the most comprehensive (and entertaining) you'll find of the game if you'd like to read more. More lies and half-truths, sure, but more nonetheless.
You can also, if you dare, check out some fan-made recreations (or... creations) of Polybius, which I'll warn you, will cause seizures regardless of your state of health.
FUN FACT: Polybius makes a cameo in a 2006 episode of The Simpsons, complete with "Property of US Government" branding .