Finding Twitter inaccessible Thursday morning, a user named Mark in Halifax, Nova Scotia, instead studied origami and recorded a cappella versions of Led Zeppelin songs. Anne in Oslo took delivery of a new refrigerator and washing machine. A user named Laura, lacking an audience for her 140-character musings, opened a Microsoft Word document and began jotting them down.

The Twitter mob has wasted little time gathering its pitchforks and circulating all manner of conspiracy theories about who is responsible.

And then, several hours later, Twitter came back online and its users began kvetching about the downtime. The cause, it is now known, was an exploit known as a “denial-of-service attack,” when perpetrators overwhelm a Web site’s servers with so many requests that they are rendered inoperative.

The parties responsible for the outage have not been identified, but the attack may have stemmed from the ongoing tensions between Russia and Georgia, a conflict that has previously spilled out onto the Internet. (Georgia says that the Russian government has been sabotaging its Web sites.) The attack on Twitter evidently targeted a single pro-Georgian blogger with accounts on a number of popular sites, including Twitter, Facebook, and YouTube, CNET News reported.

“It was a simultaneous attack across a number of properties targeting him to keep his voice from being heard,” Max Kelly, Facebook’s head of security, told CNET. “We’re actively investigating the source of the attacks and we hope to be able to find out the individuals involved in the back end and to take action against them if we can.”

The culprits still can’t be identified with any certainty, but in the wake of the outage, the Twitter mob has wasted little time gathering its pitchforks and circulating all manner of conspiracy theories about who is responsible:

1. Ahmadinejad’s henchmen. The Iranian government, so this theory goes, brought down Twitter to prevent the opposition movement from using it to organize protests after Wednesday’s swearing-in of Mahmoud Ahmadinejad. Twitter, of course, was used by Iranian protesters to organize themselves and spread information after the disputed June 12 election. “The Iranian opposition had been planning protests against President Mahmoud Ahmadinejad’s inauguration ceremony. A great deal of this planning has been over the Internet on blogs, and, of course, Twitter,” ruminated Steven J. Vaughan-Nichols in a blog post at Computerworld. “Funny timing don’t you think that Twitter would be knocked completely off the air at just this time?”

2. Facebook. Some Twitter users posted tongue-in-cheek speculation that the attack was the work of a competing social network such as Facebook. “I’m pretty sure MySpace and Facebook tag-teamed to shut Twitter down today...” one user tweeted. Facebook, however, had its own trouble staying online Thursday morning, as it was apparently targeted in the same attack.

3. Hackers in Las Vegas. Suspicious Twitter users immediately eyed the annual DEF CON hacker convention, for which thousands of security buffs descend upon the Riviera Hotel & Casino in Las Vegas to participate in seminars with titles like “Introduction to Lock Picking,” “Sniff Keystrokes with Lasers,” and “Advanced MySQL Exploitation.” One user matter-of-factly asserted: “It’s a hacker attack, people. Defcon has a conference going on. We are, apparently, the entertainment.” Unfortunately for this conspiracy theory, the four-day confab ended this past Sunday, making it unlikely that hackers lingering at the Riviera played any role in this morning’s attack.

Nicholas Ciarelli is an assistant product manager at The Daily Beast.