Reddit has been hacked
It appears someone is able to change the custom CSS at will for multiple subreddits. He also claims he has access to all reddit accounts and he's selling the 0-day for BTC.
Gaming, AdviceAnimals, fffffuuuu and iama are affected.
For example, try accessing http://reddit.com/r/gaming and you'll see a black screen with the words "Half Life 3 confirmed". Nearly gave me a heart attack.
Code for the full-screen overlay: <form action="#" class="usertext" onsubmit="return post_form(this, 'editusertext')" id="form-t5_2qh03d4n"><input type="hidden" name="thing_id" value="t5_2qh03"><div class="usertext-body"><div class="md"><p><a href="https://twitter.com/officialnea">Half Life 3 confirmed.</a></p> </div> </div></form>
Disabling custom CSS styles in your user settings will do nothing to prevent it.
EDIT: This has been posted by alienth a few days ago:
http://www.reddit.com/r/modnews/comments/205tik/mods_are_being_targeted_for_account_breakins_part/ Twitter of person/group claiming the hack: https://twitter.com/OfficialNEA Access to all Reddit accounts sounds like a huge bluff, they're selling the 0-day for 1BTC according to their Twitter.. They all look fine to me