The FBI has been raiding alleged members of the hacking collective Anonymous in recent weeks. This morning, Wired's Threat Level blogs unearthed court documents explaining how the Feds are doing that.
The bureau is working from a list, provided by PayPal, of the 1,000 internet IP addresses responsible for the most protest traffic during Anonymous' DDoS[distributed denial of service] attacks against PayPal last December.
In these kinds of attacks, groups of hackers flood a website with so many bogus requests for service the site's servers crash. Anonymous announced the attack against PayPal after that service froze Wikileaks corporate account. The hackers never quite brought PayPal's electronic system down. But, apparently, the hackers did leave a long trail of digital breadcrumbs behind, which Federal agents are now following.