Looks like Operation Payback is shifting targets from Mastercard.com to VISA. (Previous BB article here, and a related radio piece with Xeni is here.)
Update, 1:02pm PT: The Visa.com site is now unavailable. Goodness, that was fast. Post updated with a screengrab of the response I get when attempting to access visa.com. Below, a video released when Operation Payback began back in October (only recently did the focal point become companies cutting off the lifeblood of funding or internet services to Wikileaks).