A day after filing a countersuit in its hotly contested legal battle against the Universal Music Group, popular filesharing site Megaupload was shut down by the Department of Justice, sparking a flurry of activity that included indictments, arrests, and a barrage of retaliatory site takedowns led by the shadowy hacker group known as Anonymous.

It all went down on Thursday (Jan. 19), starting with the DoJ pulling the plug on the site and serving notice against several company executives, including founder Kim Dotcom (but not reported CEO and popular producer Swizz Beatz, who was not listed in the court briefs as a Megaupload stakeholder). Four arrests were made — and property was seized — at the company’s New Zealand headquarters.

That was only the beginning, however. As the day went on, a list of sites involved in the entertainment industry’s ongoing quest to defeat online piracy were taken down, including the Department of Justice, the Recording Industry Association of America, the Motion Picture Association of America, and UMG.

“It was in retaliation for Megaupload,” an Anonymous spokesperson was quoted as saying, and one of yesterday’s tweets from the Anonymous-related @AnonOps account read “One thing is certain: EXPECT US! #Megaupload.”

In the meantime, Megaupload’s many users have found themselves unable to access their files — regardless of whether or not they were being illegally shared or distributed. What’s your take on the battle between Megaupload and the entertainment industry — and how has the site going dark affected you?