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Here's what we think happened:
8-14 hours ago, an attacker used a flaw in the forum's AnonymousSpeech registrar to change the forum's DNS to point to 108.162.197.161 (exact details unknown). Sirius noticed this 8 hours ago and immediately transferred bitcointalk.org to a different registrar. However, such changes take about 24 hours to propagate.
Because the HTTPS protocol is pretty terrible, this alone could have allowed the attacker to intercept and modify encrypted forum transmissions, allowing them to see passwords sent during login, authentication cookies, PMs, etc. Your password only could have been intercepted if you actually entered it while the forum was affected. I invalidated all security codes, so you're not at risk of having your account stolen if you logged in using the "remember me" feature without actually entering your password.
For the next ~20 hours, you should only log into the forum if you're quite sure that you're talking to the correct server. This can be done by adding '109.201.133.195 bitcointalk.org' to your hosts file (remember to remove it later!), or by using some browser plugin to ensure that you're talking to the server with TLS certificate SHA1 fingerprint of:
29:0E:CC:82:2B:3C:CE:0A:73:94:35:A0:26:15:EC:D3:EB:1F:46:6B
Simultaniously, the forum has been the target of a massive DDoS attack. These two events are probably related, though I'm not yet sure why an attacker would do both of these things at once.
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TL;DR : 109.201.133.195 is probably safe, until theymos states otherwise.
