Visa, Mastercard

“IT’S DOWN! KEEP FIRING!!!” the group said in a Twitter message a few minutes later.

The Mastercard website went offline when about 400 computers targeted the LOIC software at it. By the time Visa was hit, however, there were more than 2,000 people using the software, according to Paul Mutton, a security analyst with Netcraft. Visa was a much harder target to take down, because unlike Mastercard.com, it was distributed over the Akamai Technologies network. This meant that more Visa-hosting computers had to be overwhelmed to finally knock the site offline.

Reached shortly after 1 p.m. Pacific time, a Visa representative was unable to immediately comment on the attack.

WikiLeaks supporters have hit the sites of other companies that have cut ties with WikiLeaks, including payment processor PostFinance, PayPal and EveryDNS.