A year ago this week, I wrote about how China was cracking down on social media sites in preparation for the 20th anniversary of the Tiananmen Square. This year, government censors are taking a different tack, making a flood of previously blocked sites accessible. The twist: the majority of these sites appear to be pornography.

The move directly contradicts the government's previous opposition to pornographic content online: Chinese filtering software Green Dam ostensibly exists to protect children from such content, including nude photos. Despite this, Taiwan News reports that many Chinese and foreign-language pornography sites became accessible over the past week.

Why the policy shift, and why now? The obvious answer is that the government is trying to distract Internet users from today's anniversary, though Newser's Rob Quinn reports that some believe the move may be an attempt at "calming discontent among the country's increasingly male-heavy population."

Given the number of social media sites China has blocked and its efforts to prevent discussion of the anniversary online this week, the distraction theory makes the most sense.

Facebook and Twitter, which China blocked temporarily during last year's anniversary, are less of a concern this year. Both sites have been largely inaccessible within the country since they were used to spread information about the riots in Urumqi last July. YouTube is also blocked, according to a recent flood of reports from Herdict.

This year China's decided to add location-based social networking application Foursquare to the list of blocked sites. Forbes reports that the the block came in response to the number of users who set their location to Tiananmen Square as a way of paying their respects online:

The keepers of the Great Firewall of China acknowledged the day in their own way by blocking the social networking site Foursquare. It seems that Foursquare users observed today's 21st anniversary of the massacre by telling the site in numbers that they were "checking in" at Tiananmen Square. The Great Firewall, not amused, has conferred on Foursquare its own version of the "overshare" badge.

The article also claims that Chinese social network Sina is taking candle and flower emoticons, likely posted in remembrance of the events at Tiananmen, off of its microblog.

Interestingly, among the list of newly accessible sites is video sharing site Vimeo. This has prompted some analysts to speculate that the unblocking may be a fluke. Even if it is intentional, others have noted that visits to the unblocked sites have not increased since the sites became accessible, suggesting that those who wanted to access porn from China have simply been using proxies.