Today, 4 June, is the 24th anniversary of what China calls the “counterrevolutionary riot” in Beijing's Tiananmen Square .

Much of the rest of the world records the incident as a massacre, after Chinese troops ended protests in the square by dealing out lethal force.

China now represses discussion about the events of 4 June, 1989, and extends restrictions online by declaring today to be “internet maintenance day”.

Whether sysadmins really do get the day off to install some patches and tune up their servers isn't known, but on past June 4ths several websites in China do go down for the duration of the day. The under-maintenance sites have included blogs and sites that don't always toe the party line.

A day or two after the anniversary has passed, the sites promptly finish their maintenance and get back to business.

China doesn't announce which sites will be undergoing maintenance that conveniently coincides with the anniversary, so it's not possible to know which publishers will decide to opt for a bit of downtime today.

Vulture South has tested the Twitter-like Sina Weibo and it's working, as are the MSN and Yahoo!s Chinese operations.

But dictionary site WordKu.com offers just one page: a definition for the word “encore”. We're not sure if that's a reference to previous Internet maintenance days or some other joke. If you spot a Chinese site under maintenance, do let us know. ®