Stefano Rellandini / Reuters

From sleeping dog to full-on Internet terror, it appears Anonymous may be exacting revenge on several federal and private groups after the U.S. Department of Justice (DOJ) shuttered popular download site Megaupload this afternoon, charging it with violating copyright laws.

(MORE: Feds Shut Down Megaupload.com File-Sharing Website)

Noticed by Gizmodo, the DOJ’s website went down this evening (and was still down around 6 p.m. E.T.), and a Twitter account associated with the hacktivist group was taking credit. If the attack was indeed Anonymous’ doing, you can probably chalk it up to a distributed denial of service assault (DDoS) in which someone attempts to knock another computer offline by completely overwhelming it.

And it’s not just the DOJ’s site that’s down — it appears Universal Music Group’s website is down (or stuttering), along with the MPAA (Motion Picture Association of America), the RIAA (Recording Industry Association of America) and the U.S. Copyright Office.

[Update @ 6:33 p.m. E.T. — Anonymous is claiming credit for taking down BMI’s website (music royalty, publishing and licensing group). Gizmodo also says a Russian news service is claiming that “this is the largest coordinated attack in Anonymous’ history — over 5,600 DDoS zealots blasting at once.”]

[Update @6:45 p.m. E.T. — It looks like Anonymous is globe-trotting: The website for French copyright-enforcement agency HADOPI is down.]

FOLLOW-UP: 10 Sites Skewered by Anonymous, Including FBI, DOJ, U.S. Copyright Office