So what should you do now? Do you need to change your password? Is your account compromised?
No, it's not. 'Rachel' sent PMs like any member can do; s/he just sent a whole lot of them, most likely to usernames that were visible in the forum. It must have been a lot of work, since we do not have a mass PM option (and this is exactly why).
There is nothing you need to do now. 'Rachel''s accounts are blocked. You can just delete the PM... or print it out and embroider it in cross stitching to frame it and hang it over your computer, if you like. It's up to you.
In all seriousness: our thanks to those who reported it as soon as it happened. That was very helpful. Now we can all go back to our daily BookCrossing lives!