An intrepid computer scientist at the BBC has been quietly whittling away at one of the Web’s greatest mysteries. There are, admittedly, a lot of contenders for that title — but the case of “Webdriver Torso” is particularly puzzling.

Webdriver is a YouTube channel with a simple, impenetrable premise. Every hour or so, the channel posts a new 11-second sequence of red and blue boxes moving around the screen. The account ran from September 2013 until mid-April, when it mysteriously stopped; recently, the uploads have begun again. According to one theory, the channel could be a modern “numbers station” — cryptic radio signals used during the Cold War to send messages to spies. According to another, the videos are communications from aliens.

Which is it? Frankly, we don’t know. Even after analyzing all the data for the nearly 80,000 cryptic, 11-second videos on Webdriver Torso’s YouTube channel, the BBC’s Stephen Beckett could only conclude that the videos were — maybe possibly — uploaded from France. No sign of who’s behind them. No suggestion why they started. And, most infuriatingly, not even a hint at what they mean.

“If it is indeed aliens,” Beckett’s forced to conclude, “let’s hope they … come in peace.”

It would appear aliens are doing a lot of messaging these days: The Internet has no shortage of weird, cryptic codes and mysteries. These are just some of the most stubborn.

Cicada 3301: For over two years, amateur cryptographers have struggled with Cicada 3301, a kind of Internet scavenger hunt that relies on advanced code-breaking — and a working knowledge of things like obscure medieval literature and Mayan numerology — to unlock progressive clues. Who’s behind the puzzle is unclear, although many enthusiasts believe it’s a large, well-funded and shadowy organization trying to recruit into its membership. At this rate, we may never know.

The Markovian Parallax Denigrate: Early in Internet history, a community called Usenet got spammed, repeatedly, with SAT-word mumbo jumbo that reached “an almost transcendent level of bizarre.” Each post was titled “Markovian Parallax Denigrate,” and none of them made any conceivable sense. Generations of Internet sleuths have, over the past 15 years, tried to decode the messages or pin them to a government operative, with middling success. The Daily Dot concluded — in an exhaustive, fascinating piece that’s really worth reading in full — that the whole thing was probably the work of “a troll or prankster.” Then again, we still don’t really know!

A858: Since 2011, a (potentially robotic?) Redditor named A858DE45F56D9BC9 has posted long, coded strings of text to a sub-Reddit of its own making. Thousands of people have devoted themselves to interpreting the posts; there is even a program, A858StatsBot, that automatically calculates information like message length and statistical distribution for would-be decoders. Wrote the bot’s creator, in a GitHub post: “A858 is maybe the biggest mistery [sic] on Reddit.”

Bitcoin: This particular puzzle does not, perhaps, rise to the level of otherworldly creepiness that things like Cicada and A858 do. Nevertheless, the question of who created the cryptocurrency Bitcoin remains stubbornly unanswered — despite many attempts to out the man known as Satoshi Nakamoto.

There is, of course, only one thing even more frustrating than an impenetrable Internet mystery: When such a mystery is solved, and the solution is … stupid. The YouTube channel Pronunciation Book, c. 2010 – 2013, abruptly began counting down to an unnamed big event last July. Was it some nefarious NSA messaging? A sign of the coming apocalypse? Nope, just part of the whole @Horse_ebooks circus/”conceptual art project.”

Fans were, shall we say, not pleased.