Three of the web's most popular social networking websites - Facebook , Twitter and LiveJournal - were both targeted in malicious Distributed Denial of Service (DDoS) attacks Thursday morning. Twitter first acknowledged that their downtime was a result of a DDoS attack, followed sometime later by Facebook, and then LiveJournal.

During the attacks, Twitter was completely inaccessible to users. Facebook fared a bit better and worked, although not completely. Facebook users encountered quite a few errors rather than an inability to access the site altogether. LiveJournal users also encountered a number of problems.

What does this mean? This was a deliberate attempt by some nefarious group to take down three of the most popular social media sites. Given the strength and size of the infrastructure of these sites, the attacks had to have been coordinated and planned for months.

It's likely that the FBI will jump in to investigate the origin of these attacks today. Just when we the public might find out who was behind it, however, remains to be seen.

There could be other sites out there as well that were or are still affected. Have any of your favorite social media sites been acting funny today? Let us know in the comments.