Microblogging site Twitter has been hacked by a group of protesters calling themselves the Iranian Cyber Army. The attack forced Twitter offline for more than an hour overnight, leaving Twitter users unable to log on to the service or send tweets.
Visitors to Twitter.com were automatically redirected to another web page, which displayed a green flag and English and Arabic writing.
"This site has been hacked by the Iranian Cyber Army," read the message. "The USA thinks they control and manage internet access, but they don't. We control and manage the internet with our power, so do not try to the incite Iranian people."
Twitter said that a DNS attack – where a web address is diverted to another site – was to blame for the outage.
"Twitter's DNS records were temporarily compromised tonight but have now been fixed," wrote Biz Stone, Twitter's co-founder, in a blog post. "As some noticed, Twitter.com was redirected for a while but API and platform applications were working. We will update with more information and details once we've investigated more fully."
Twitter was widely used by Iranian citizens protesting against what they believed to be an unfair election result earlier this year. The microblogging service even delayed a period of planned maintenance so that the site could stay online, giving protesters the ability to communicate with those outside Iran.
It is unlikely that any computers were infected or compromised after being redirected to the hacker's website, said Graham Cluley, a security expert with Sophos. He said that there was "no indication" that the page Twitter users were redirected to carried malicious code that could have infected computers.
"This attack appears to have had political motivations rather than been designed to steal confidential information from users," he wrote on his blog. "Of course, just because a message saying 'This site has been hacked by Iranian Cyber Army' has been posted on a webpage does not necessarily mean that hackers from Iran are responsible for the defacement.
"However, Twitter was widely used earlier this year by those wishing to share information about anti-government protests [in Iran], and rumours spread in July that planned maintenance on the site was delayed to allow Iranians to continue to share information from inside the country as citizen journalists commented on the controversial election result."
Twitter said that normal service had been restored.
