Who is Anonymous?

There's been a lot of news over the past few days about the hacker collective Anonymous. Last Friday, the group claimed to have posted an internal FBI conference call discussing investigations into Anonymous and the FBI acknowledged the call was intended to be private. This week, Anonymous posted e-mails that it claims are from an adviser to the Syrian president, suggesting how Bashar al-Assad could downplay violence in the country when he was interviewed by Barbara Walters last summer.