The internet was apparently baffled yesterday when Google changed its logo to show a UFO abducting one of Google’s Os. Our story on the “mystery” is currently our most-viewed technology story, with 220 comments.

While some of our readers are speculating about whether Google has made contact with aliens (or are in fact aliens themselves) most people are working on the theory that Google’s logo usually changes to mark an anniversary of some kind. Perhaps the UFO reference marks the release of the scifi film District 9, a few readers suggested? Perhaps, but the film was released on September 3 and Google changed its logo a day later, so we can dismiss that.

“Today is the anniversary of the launch of the Voyager I spacecraft,” pointed out Kelso, correctly.

But if that was the link then why did Google link their logo to a search for the term “unexplained phenomena”? “Maybe this is their way of suggesting that some aliens wanted to find where it came from?” asked Kelso, going out on a bit of a limb.

Google offered a clue on its Twitter page, adding the message “1.12.12 25.15.21.18 15 1.18.5 2.5.12.15.14.7 20.15 21.19″. Swap those numbers for the corresponding letters of the alphabet and you get “All your O are belong to us”.

Now we’re getting closer. As several readers explain, that phrase is a reference to an internet meme that did the rounds a few years back. The phrase “All your base are belong to us”, a poorly-translated line from a Japanese video game, popped up in all kinds of internet jokes. So why is Google reviving the gag now?

Well the game the line is taken from, Zero Wing, was first released in Japan on September 5, 1989 - 20 years ago yesterday. Happy birthday Zero Wing. And congratulations to Blasphemy101 who got very close to the answer but got the release date wrong and to Brian who noted that Zero Wing was released in September 1989.

Update: As Andrew Healey points out below, the release date for Zero Wing was added to Wikipedia today. Before that edit the release date was simply given as “1989″. Of course, that doesn’t mean it wasn’t released on September 5, 1989, but it doesn’t prove it either. Back to square one? Andrew has other discredited theories on his blog.