The US intelligence agency, the FBI, has seized servers that they believe launched distributed-denial-of-service (DDoS) attacks against financial firms like VISA and PayPal after they stopped supporting Wikileaks.

The Smoking Gun website posted a five-page FBI affidavit, which provides details of an operation in which the US federal investigators hunted for the hacker in the US, Europe, Canada.

The operation by the US federal investigators was launched after a group of hackers, called Anonymous, triggered a series of DDoS attacks against several agencies and financial companies, which had stopped supporting WikiLeaks after the whistle-blowing site exposed thousands of sensitive Department of State cables.

The US federal investigators raided the Texan hosting firm Tailor Made Services firm in mid-December. The firm obtains material from government and law enforcement sources using Freedom of Information requests.

Investigators are advancing on the assumption that some used botnets of compromised machines to trigger potent distributed-denial-of-service attacks against PayPal, knocking these sites offline for several hours.

4chan, web forum used by Anonymous, recently suffered distributed-denial-of-service (DDoS) counterattacks.