A "denial-of-service attack" or DoS attack is a cyber attack on a website. During a DoS attack, a website is flooded with phony requests. Due to the massive spike in website traffic, the website simply cannot keep up and legitimate users are unable to log in. The social networking website Twitter and the gossip blog Gawker were both crippled by a denial of service attacks on August 6, 2009. On the same day, Facebook was experiencing similar problems. 
via mahalo.com
My first clue that Twitter was down was the ugly red "t" on my Twitter fox. I wonder how many of my tweets were lost in space? Facebook is still wonky (around 1pm on Thursday) I hope its better later because I have to decorate my house in YoVille :)
