Thursday night, Iranian activists hacked Twitter. The site was down for nearly an hour, leaving millions of people tweetless. Several users, who did log in reported seeing a green flag on the site, the same color that is used by the Iranian opposition movement.

Reportedly, twitter has admitted that its systems were down temporarily, but the problem has now been fixed.

During the Iranian elections earlier this year, the site was used extensively by anti government activists. The US State Department requested twitter, in june, to delay its planned maintenance work which would have resulted in interruption of service due to the crucial role that the site was playing in spreading information about protests.

Earlier this week, Twitter declared that “#iranelection”, the “hashtag”, used by its community to track messages from and about Iran, was the top most topic among news events, and the second most commonly used hashtag this year overall.

Although many Twitter users reported seeing a green flag alongside a message from a group claiming to be the “Iranian Cyber Army”, but it is still difficult to verify who the attackers really were.

Moreover, this security breach is not the first one for Twitter. Several celebrities, including Britney Spears, have already had their accounts hacked.

It is being said that the disruption was caused mainly due to the increasing efforts of Twitter to commercialize the service, which already has more than 30 million users.