If a tree falls in the woods but no one Tweets about it, does it make a sound? The Twitterverse was inaccessible for several hours Thursday morning due to what the company is calling an "ongoing" denial-of-service attack, which occurs when hackers overload a site's infrastructure with data. Twitter's problems began around 9 a.m. EST, with its inaccessibility period followed by continuing slowness and timeouts. Facebook, too, experienced hang-ups Thursday, while URL shortener Tr.im said a similar attack Wednesday rendered its service unavailable, and blog network Gawker Media crashed earlier this week. There is no evidence that these attacks are connected, CNET reports, but it's likely no coincidence that they overlap with the annual Defcon hacker convention. Dryly commenting on Twitter's unexpected downtime, The Associated Press reported, "the outage means no tweeting about lunch plans, the weather or the fact that Twitter is down."