Some person of a trollish nature has written a script to friend anyone on the 'recent posts' page. (How do I know this? Because a troll friended me. I am more creeped out by this than it really warrants.)
There are two ways that you can fix this kind of serial adding:
1: pre-emeptively.
Go to the
Admin Console and type in "set latest_optout yes" (without the quote marks). This will keep your latest posts from appearing on the recent posts page, and so the script will never pick you up. Quite possibly a good idea anyway.
2: ban_set username.
Go to the
Admin Console and type in "ban_set username" (without the quote marks), with the username of the journal you wish to ban replacing 'username'. This bans them from commenting in your journal (although they can still post anonymously) and also removes you from their friends list.