After Mastercard.com had been attacked, visa.com was attacked too just now. And they all was down for some place and some time. The reason is that they are against wikileaks.

This attack method is called DDOS (Distributed denial of service attacks).

Here is the explaination of wikipedia.org

Distributed denial of service attacks on root nameservers are Internet events in which distributed denial-of-service attacks target one or more of the thirteen Domain Name System root nameservers. The root nameservers are critical infrastructure components of the Internet, mapping domain names to Internet Protocol (IP) going to and other information. Attacks against the root nameservers can impact operation of the entire Internet, rather than specific websites.

It doesn’t damage the data in the targeted server generally. Just the server is so busy to answer the requests from the attackers that they can’t share any time to answer the requests from the real users when the server is attacked. When the attack stops, the server can be recoverd soon generally.

This attack needs a lot of attackers to send those fake requests to the targeted server at the same time.

Here is an example how the “Operation Payback” gethered their volunteer soldiers and started their cyber fire on twitter:

 

About 6 hours later, another tweet:

@Anon_Operation Operation Payback