Twitter went down for a number of hours yesterday as a result of what it calls, “a single, massively coordinated attack.”

Hackers launched what is known as a denial-of-service attack on the micro-blog. "Attacks such as this are malicious efforts orchestrated to disrupt and make unavailable services such as online banks, credit card payment gateways, and in this case, Twitter for intended customers or users," said Twitter co-founder Biz Stone in a blog post yesterday.

Facebook was also targeted by the as yet unidentified hackers, but their service was not forced to go offline.

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Hackers attack Twitter, Facebook also slows down