Last August 6, Twitter had a distributed denial-of-service (DDoS) attack, along with Facebook, LiveJournal and YouTube. It was believed to target a pro-Georgian blogger whom attackers wanted to silence him with an act of hacktivism.
It proved not to be an isolated case as another DDoS attack was launched on Twitter.
Around 3 PM EDT, Twitter posted a status blog stating that it was experiencing a site outage and was currently examining its nature.
It announced later on through a post on their bulletin board that it was indeed, another DDoS attack.
Alex Payne, platform lead at Twitter warned users in the post to “Expect periodic slowness and errors until the attack passes or is countered by our operations team and hosting provide.”
The attack yesterday didn’t last long but according to Payne, the attack resumed in the later part of the day.
A distributed denial-of-service attack is an attempt to make a computer resource unavailable to its intended users.
Source: http://www.eweek.com/c/a/Security/Twitter-Attack-Knocks-Out-Service-Again-328455/