Turns out two can play that game.
The Twitter account of the hacker group Anonymous' 'Operation Payback' appears to have been blocked. The pro-WikiLeaks group has been linked to payback takedowns against companies that have suspended access to fund-raising for WikiLeaks--including MasterCard and Visa.
Twitter declined comment.
Earlier, the group hit MasterCard's website with a distributed denial-of-service attack and took down PayPal over the weekend. The MasterCard site was back up this afternoon.
"IT'S DOWN! KEEP FIRING!!!" the group tweeted on its Operation Payback campaign page.
On Wednesday, Visa suffered intermittent downtime, one day after preventing people from making payments to WikiLeaks.
(This report included reporting by CNET's Elinor Mills)