The portal of US communications giant Comcast was hacked on Wednesday night in an assault that left subscribers unable to access their emails for several hours.

The comcast.net front page was replaced by a greeting from hackers on Wednesday night (28 May). The defacement was removed around two hours later. Users were then confronted by a "page under construction" message before the site was restored in the early hours of Thursday morning. The site remained intermittently unavailable even after this time.

The defacement was claimed by hackers calling themselves KRYOGENIKS Defiant and EBK.

As a result of the attack Comcast subscribers were unable to access their email or other services through the portal for more than two hours. Comcast is the second biggest ISP in the US and a major provider of cable TV services.

Comcast.net runs using unknown web server software on a Linux platform, Netcraft reports.

The exact mechanism of the attack is unclear, though an injected iFrame that served up content from sites under the control of hackers is suspected. Some form of DNS redirection attack may also have been involved.

A Comcast spokeswomen said she was looking in to the matter.

Normally defacement attacks simply involve the spraying of digital graffiti on a website. However, in the case of the Comcast attack it seems some attempt may have been made to snoop on its users' login credentials.

"There is still a lot of speculation about the details of this and why this happened," said Comcast user and Reg reader Chris, who first brought the attack to our attention. "But it is clear now that a group of people (according to the hacker's message) somehow rerouted the IP and DNS values of Comcast to an off site. (http://www.freewebs.com/kryogeniks911/)."

"It appears there was no malicious codes or script being run but a lot of people are saying that ports were being 'listened' to which could have led to the compromising of username/passwords," he added. ®