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The Ubuntu forums software was compromised by an external attacker. As a result, the attacker has gained access to read your username, email address and an encrypted copy of your password from the forum database.

If you have used this password and email address to authenticate at any other website, you are urged to reset the password on those accounts immediately as the attacker may be able to use the compromised personal information to access these other accounts. It is important to have a distinct password for different accounts.

I haven't kept a list, but this is becoming horribly common.

Seems like if you don't have two-step authentication, you don't have any authentication at all.