Some people on my F-List (and me as well) have been getting pop-ups from Avast! Anti Virus while on LiveJournal and some other sites that are screaming at us about OMG TROJAN, VIRUS, RUN, RUNNNN FOR THE HILLS!
>>>>>
No, it's not a virus. Avast! fails and fucked up their newest update.<<<<<
You can ignore the pop-ups, which is... annoying. Or use FireFox and the NoScript add-on to block the JavaScript that's fucking it up until Avast! fixes their shit.
EDIT: Updating Avast! will now solve the problem if you've encountered it :3