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For the past seven months, a single YouTube channel has been uploading an average of one video every 20 seconds. Each video is exactly the same: 10 seconds long, they flick through 10 still images of a blue and a red rectangle, accompanied by a series of electronic tones. The position and sizes of the shapes, the title of the video and the pitch of the tones all appear to be completely random, but every single video has the caption "aqua.flv" in the bottom-left corner.

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The 77,000 or so videos have all been uploaded by an account called "Webdriver Torso", and the hunt for their creator – and purpose – has entranced the internet for a week. Theories ranged from alternate reality games to extraterrestrial activity, through espionage and viral marketing. The Today programme took to Twitter to blame either aliens or advertising:

"The aliens are coming" says @1357marty about mystery videos: http://t.co/VWKl7YPwtf. @thehugheslady thinks its an advertising campaign

— BBC Radio 4 Today (@BBCr4today) May 1, 2014

While on the blog BoingBoing, user Enkidu speculated that the videos might be a digital version of spies' "numbers stations". These cold war relics are radio stations that broadcast seemingly random numbers at periodic intervals. They are thought to be the basis of a method of encoded communication using what are known as "one-time pads", large sheets of random data that let spies create unbreakable messages (so long as the one-time pad never falls into enemy hands). Could the Webdriver Torso videos be fulfilling a similar purpose?

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The Daily Dot's Brendan O'Connor tried to track down the videos' creator, but to no avail; whoever is behind the YouTube account ignored his messages, and didn't respond when the Guardian attempted contact either. But O'Connor did find a company called Selenium that makes a product called Selenium Ice, which has a function called … WebDriver. The software is used to automate testing websites, but even its creators don't know what the videos are about. As O'Connor reported:

It looked likely that "Webdriver Torso" was part of this project, not only because of the shared neologism but also because automation seemed like the only plausible explanation for uploading this quantity of video. But Patrick Lightbody, who has been involved with Selenium since 2005, denied that there was any connection between their WebDriver and Webdriver Torso. "Those videos look like they are trying to make contact with aliens," he wrote.

But the truth is, as ever, more mundane.

Isaul Vargas, a New York-based software tester, spotted the videos in a post on BoingBoing and recognised them from an automation conference he had been at a year ago. They were being shown by a European firm that made streaming software for set-top boxes, the kit that sits under a TV and connects to services such as Sky or Netflix.

The company needed to be able to quickly and reliably upload digital video, a capability which it tested by uploading short, randomly generated snippets to its YouTube channel and running image-recognition software on it. "Considering the volume of videos and the fact they use YouTube, it tells me that this is a large company testing their video encoding software and measuring how Youtube compresses the videos," says Vargas.

So there's the answer. What looked like an insight into the murky world of espionage, or maybe even something otherworldly, turns out to be a little bit of a quality-control system leaking into the outside world.

Perhaps some puzzles are better left unsolved.

UPDATE: But there's another twist. Isaul has tracked down the presentation he saw, which was given by the British company YouView. While it features similar videos, it is not identical: so although the general principle of using WebDriver, YouTube and automatic image recognition to test software stands, the culprit has slipped off into the night.

When one door closes, another opens. A thousand videos into the series is one six-second clip that breaks the mould. A short video of the Eiffel Tower, it features a comment from the uploader: "Matei is highly intelligent." Already, readers have been hard at work trying to find someone who fits the bill, but it's tricky. Matei is a common Romanian name, and even assuming that Matei is the uploader, is based in France, and has a public profile, there are at least two possibilities: Basarab Matei, who works on image recognition at the University of Paris North (suggested by @DAddYE), and Matei Mancas, who works on attention modelling at the University of Mons in Belgium (suggested by @marquis).

The Guardian has asked both if they can shed more light on the question, but has yet to receive a reply.