I wrote a script that counteracts 3 kinds off messenger spam:
1. People nudging you while they are offline
(it sends a message not to do that any more and blocks them for a while)
2. People adding you to huge groupconvo's
(it sends a message not to do that any more and closes the convo)
3. People sending you too much messages
(it sends a message not to do that any more and blocks them so they can't send anymore messages)
edit:
added in 1.1:
4. People sending you too much nudges
(it sends a message not to do that any more and blocks them so they can't send anymore nudges)
5. People signing in too often
(it sends a message not to do that any more and blocks them so the signin spam won't bother you)
This is the beta version so you might encounter some bugs..
If so please inform me so I can fix them...
you can download it
here
or you can use the attachment