Twitter was knocked offline again on Tuesday, the second prolonged outage affecting the popular microblogging site in less than a week. The company did not immediately know the cause of the latest service interruption, only stating in its Status blog that, "We're back up and analyzing the traffic data to determine the nature of this attack." The site was down for about 20 minutes on Tuesday, starting around 3 p.m. EST. Last week's downtime, which lasted a couple of hours, was traced to distributed denial-of-service attacks launched against the Twitter account of a pro-Georgian blogger. Facebook and LiveJournal also were hit but did not sustain any significant downtime. — DK