Yesterday was a big day for those protesting the Stop Online Piracy Act, including several large websites being blacked out and many discussions had using social media. Today, Twitter announced that 3.9M Tweets about SOPA had been sent yesterday, January 18th.

At 4PM Eastern yesterday, Twitter reported that there had been 2.4 million Tweets about the controversial censoring act. The top terms that were being used were SOPA, Stop SOPA, PIPA, Tell Congress and the humorous #factswithoutwikipedia.

Wikipedia had shuttered its site with a notice about SOPA yesterday, causing many to take to Twitter to comment or complain about its closure. Many of the more clueless Twitter responses to the blackout were catalogued by the Twitter account @herpderpedia, run by Nick Quaranto of 37 Signals.

Wikipedia’s blackout ended up driving 14% more visitors to its mobile site (which was not censored) in the UK yesterday.

Twitter’s CEO and co-founders also took to the service yesterday to express their own stance on SOPA.