Users trying to reach Twitter early Friday were redirected to a Web page that CNN reported had a picture of a green flag and a message that said, "This site has been hacked by the Iranian Cyber Army."
There was no evidence the hackers are actually linked to Iran. Web sites like Twitter and Facebook helped bring attention to the Iranian opposition during the country's crackdown after its June elections, with users posting minute-by-minute updates and amateur video.
Twitter later Friday posted a message on its blog that said its Domain Name Systems' records "were temporarily compromised but have now been fixed." The site says it will update with more details "once we've investigated more fully."