From the story:
The FBI investigation began earlier this month after PayPal officials contacted agents and “reported that an Internet activist group using the names ‘4chan’ and “Anonymous” appeared to be organizing a distributed denial of service (“DDoS”) attack against the company,” according to an FBI affidavit excerpted here.(found via Neon Tommy)
The PayPal assault was part of “Operation Payback,” an organized effort to attack firms that suspended or froze WikiLeaks’s accounts in the wake of the group’s publication of thousands of sensitive Department of State cables. As noted by the FBI, other targets of this “Anonymous” effort included Visa, Mastercard, Sarah Palin’s web site, and the Swedish prosecutor pursuing sex assault charges against Julian Assange, the WikiLeaks founder.