There has been an attack.
LJ Security Alert!
"There's been a breach of LJ security using embedded content, where post entries are edited to be public and contain malicious flash content".
The malicious code got into your LJ if you clicked on embedded content, worryingly it then make your private LJ posts public and reset your icon to the default, while also gleaning your email address. More grisly details from LJ themselves
here Thanks to
dahliablue for the heads-up. Am reposting for all those who had issues earlier.