Hackers claiming allegiance to the amorphous Anonymous movement say they've defaced several sites belonging to online defense firm Panda Security.

Anonymous supporters have been rattled by a trans-Atlantic investigation that has exposed one of the group's best-known hackers, Sabu, as an alleged FBI informant.

U.S. and British officials charged six men and one adolescent with a host of computer crimes linked to Sabu's activities Tuesday, sowing anger and confusion among supporters of the loose-knit network.

But the group fired back with an attack against dozens of Panda Security subsites, accusing the company of working with law enforcement.

The Bilbao-based Panda Security said Wednesday its main site wasn't compromised.