Washington, Aug 7 (DPA) Unidentified hackers brought the microblogging website Twitter to its knees for several hours Thursday.

Twitter founder Biz Stone said the site, which was down altogether for about two hours, had suffered a so-called 'denial of service' attack.

'We are defending against this attack,' Stone said.

He added that Twitter would continue to update its site even though it remained under attack, and noted that the situation would be subjected to an investigation.

In a denial of service attack, hackers try to prevent access to a site by overloading it. As Stone explained, this kind of attack is most often used against online banking and credit card systems.