The Interpol Website, via "Liquid Mud" BlogThe inherently political nature of the activity, the short lead-up time to the arrests, and the (alleged) dynamics of the group are all interesting. From the NY Times:

The arrests followed an ongoing investigation begun in mid-February, which comprised searches of 40 locations in 15 cities and included the seizure of 250 pieces of information technology equipment and mobile phones, Interpol said.

Among the 25 people arrested were four suspected Anonymous hackers seized in connection with attacks on Spanish political party Web sites, the Spanish police announced. A national police statement said two servers used by the group in Bulgaria and the Czech Republic have been blocked. It said the four arrested included the suspected manager of Anonymous’s computer operations in Spain and Latin America, who was identified only by his initials and the aliases “Thunder” and “Pacotron.”

The four are suspected of defacing websites, carrying out denial-of-service attacks and publishing data online about police assigned to the royal palace and the premier’s office.

Anonymous has no real membership structure. Hackers, activists, and supporters can claim allegiance to its freewheeling principles so it is not clear what impact the arrests will have. Some Internet chatter appeared to point to the possibility of a revenge attack on Interpol’s Web site, but the police organization’s home page appeared to be operating normally late Tuesday.