Pretty Little Liars season 2 finale “Unmasked” generated the most social media traffic of any regularly scheduled series in the history of television.

The series is number one for female demographics aged 12 to 34 during its time slot (the show airs on Mondays at 8 p.m. ET); it is also the number one scripted cable show so far in 2012 for the same demographic.

The first showing became one of Twitter’s biggest hours ever, “Fans sent a whopping 645,000 tweets during the first broadcast, hitting the 32,000 tweets per minute mark. Over the course of the day (a catch-up marathon was playing), 1.6 million tweets were sent by 667,000 users.”

Some 50 topics — including five worldwide trends: Ezra, Garrett and Melissa, Spencer, Mona or Jenna, and Black Swan — trended on Twitter Monday.

“We’ve been tracking tweets about television shows and events for several years, and this is one of the biggest hours of TV on Twitter we’ve ever seen,” Jenn Deering Davis, founder of TweetReach, said. “Pretty Little Liars is consistently among the most active shows we track, and [Monday] night’s finale eclipsed the show’s previous high of 289,000 tweets during one show.”

The series follows the lives of four girls — Hanna Marin, Spencer Hastings, Emily Fields, and Aria Montgomery — whose circle falls apart after their leader, Alison DiLaurentis, is classified as a missing person. Three years later, when the girls are juniors in high school, Alison’s body is found, and they begin receiving threatening messages from someone using the alias “A.”

After the girls are told that they will be avenged and exposed they band together in a quest to find their friend’s killer.

Each of the actresses have a strong following on Twitter and generated interest in the finale by tweeting clips of the show, asking followers about their favorite moments, and sharing updates from the set.

The following YouTube video dishes the details of the finale, but beware, this will spoil the surprise if you haven’t already watched the episode:

Viewers tweeted after the finale: