The whole team is aware and since hours the Volunteer Support Team is doing all they can in blocking spammy accounts that you are reporting!
I've been on the road for a few hours but meanwhile have done some investigation.
I'll report in more detail later (don't hold your breath, may not be today ...).
Right now I rather spend my time breaking this wave.
==== 1st. short update: ==
a) After some analytic I've blocked those spam accounts by different methods.
Those spammy Friend Requests have instantly stopped.
However, to some extent I had to use emergency measures, which means that may turn out not to be thorough enough, we'll see tomorrow ...
b) All suspicious Friend Request have been removed (of course not the emails that already have been sent out ;-> ), even if they already had been accepted.
c) It appears that those spammy accounts in fact have formerly been accounts of BookCrossers "in good standing", some even with books registered etc.
Apparently their accounts have been "hijacked", most likely because they were re-using credentials (email + password) that they've used elsewhere and where those have been stolen from.
I've checked a sample of those accounts against https://haveibeenpwned.com/ and almost all of them were hits, some credentials were found in even more than 10 breaches that happened throughout the past years!
==>> Don't use the same combo of email-address/login-name and password on different websites!
==>> Change your password(s) *now* if you realize you're re-using them in different places!
==== Next Morning update ==
Turns out they've indeed changed their strategy and since a few hours they've started again.
I may need to fully disable sending Friend Requests for now.
If that happens there will be a separate Announcement.
==== Update: ==
Sending Friend Requests has been - supposedly fully - disabled for now.
[Note from Support - we no longer need members to report these Friend Requests via Contact Us. Thank you]