The investigative site, TheSmokingGun, has secured an FBI affidavit revealing that on December 9 PayPal security officials provided the U.S. government with a number of IP addresses which they allege were used as a platform for the online attacks waged by the groups called Anonymous and 4chan.  The hacker groups took down several financial sites whose parent companies had suspended or terminated money transactions to the WikiLeaks group. Among them were PayPal.

The retaliatory attacks were dubbed Operation Payback. The FBI moved in a week after being given the leads from PayPal.  

The SmokingGun Reports:

Investigators traced the IP address to Tailor Made Services, a Dallas firm providing “dedicated server hosting.” During a December 16 raid, agents copied two hard drives inside the targeted server. Court records do not detail what was found on those drives, nor whether the information led to a suspect or, perhaps, a continuing electronic trail. In a brief phone conversation, Lynd declined to answer questions about the ongoing denial of service probe.

Search warrant records indicate that agents were authorized to seize records and material relating to the DDoS attacks “or other illegal activities pertaining to the organization “Anonymous” or “4chan.”
A second IP address used by “Anonymous” was traced to an Internet service provider in British Columbia, Canada. Investigators with the Royal Canadian Mounted Police determined that the Canadian firm’s “virtual” server was actually housed at Hurricane Electric, a California firm offering “colocation, web hosting, dedicated servers, and Internet connections,” according to its web site.

See the FBI affidavit here.