LulzSec, six of whose members were arrested earlier this month, will resume hacker operations on April 1, while Anonymous declared independently security firm Imperva are one of their targets.

"It's ridiculous to believe that by arresting the six prime members of LulzSec that you have stopped us," said the electronically altered voice over in a video posted on YouTube. "You haven't stopped us. You have merely disrupted the active faction."

The video doesn't specify who will be attacked other than that they will be from categories of organisations that it has attacked before: websites of governments, corporations and agencies. "As we speak our battle fleet and dormant members are planning some top operations and pranks that will go down in history," the video voiceover continued.

LulzSec claimed a string of attacks during 50 days last spring before disbanding, and some of its members shifted over to the even more amorphous group Anonymous.

Meanwhile in a separate video Anonymous has declared security firm Imperva a target of its activities. "This is a message to the Imperva security firm. Although we do not see you as any form of threat we have determined that your interests and views may become a mild nuisance in the future therefore you yourself will become a target," an electronically altered voice said.

What set Anonymous off was Imperva's report about an attack Anonymous made to disrupt an unnamed event in 2011. Contributing to the decision to attack Imperva was apparently hurt feelings. "A video posted on YouTube states that Imperva perceives a large majority of the Anonymous collective as, in their words, "a legion of idiots", according to the Anonymous video.

The video is a report by Jason Unruhe who actually reads a quote from Cole Stryker, who has written a book about Anonymous, that appeared in The New York Times on February 26. "Anonymous is a handful of geniuses surrounded by a legion of idiots," said Cole Stryker, an author who has researched the movement," the NYT story said. The story also identifies the target of the Anonymous attack that the Imperva report talks about as being aimed at the Vatican.