Roger Dingledine was looking at usage statistics for Tor earlier this week when the project lead for the anonymous browsing software noticed something odd: The number of people connecting to the Tor network seems to have taken off.

(The Tor Project)

After running some checks, Dingledine confirmed that the spike wasn't just a fluke. There really are twice as many instances of the Tor software running than before. The question is, why?

If you're unfamiliar with Tor, the service is actually a package of products that users can download and, once enabled, lets them surf the Internet privately. (Tor has a more technical explainer here.)

Several days later, the spike is still ongoing. And its origin is still a mystery. While American concerns about NSA surveillance might come to mind at first, it's clear the United States isn't driving the surge. This month U.S.-based connections to the Tor network rose by 50 percent, but that wouldn't be enough to account for such a sharp global increase in Tor usage.

Some have suggested that a recent Russian anti-piracy law is driving people to the service. The new law, which has been compared to the United States' SOPA and PIPA bills, allows the government to shut down Web sites that are the subject of copyright complaints. An e-mail in a Tor-related listserv suggests that Russian users have been flocking to Tor since the law went into effect on Aug. 1.

Russia's connection graph does reflect a doubling, but its absolute numbers are, like the United States, still too low to make a huge impact. The rise is clearly more distributed across a wider range of countries. Here's what the increase looks like from Britain. And India, Brazil and Germany all posted significant increases, too.

Could it be rebels from Syria getting savvier with technology? Not likely, as Tor has been popular in Syria for years:

(The Tor Project)

Maybe it has something to do with Google's decision to open up its app store to Iran, enabling Iranians to download the new Tor app for Android, some said. But Iran has reportedly blocked access to the Play store already.

The prevailing theory right now is that thousands of people are downloading The Pirate Bay's new Tor-powered browser. The Pirate Browser, as it's called, only helps users get around a country's Internet censorship; it doesn't provide anonymous browsing like standard Tor does. Still, because the tool relies on Tor's routing technology, rapid adoption of The Pirate Browser could have led to many more connections to the Tor network. To see whether that theory holds, keep an eye on the connection chart. If the numbers don't drop off, then it could mean that users of the Pirate Browser have decided to stick with the application.