This MIGHT be strange for e-mail and LJ... but I know with World of Warcraft you have to watch out for these programs called keyloggers. They're often embedded in suspicious flash files and linked off warcraft forums and websites. If it infects your computer it records your keyboard movements and eventually passes off your user name and password to a third party who hacks into your account and steals all your gold (Warcraft gold can be sold for real world money, though it is illegal).

I wonder if there's a similar program that hijacks e-mails. Might be handy for credit card fraud or accessing anything those e-mails are tied to. (I'd guess with the aim getting into finacial stuff)

Of course, it could just be some crazy internet stalker. But I'd try running your virus protection and perhaps an anti spyware program like adaware or spybot.