No it does not purge old links but it should block them from being accessible.
ALWAYS HAVE A DATABASE BACKUP BEFORE RUNNING A MANUAL QUERY- This is untested, use at your own risk.
I would try-
Code:
UPDATE user SET homepage = '' WHERE homepage <> '' AND posts < 10
That should update the user table, it will set the homepage field to blank for any user where it isn't already blank who has less than 10 posts.
If you really want to wipe it out for everyone completely, including admins/mods then the query is just-
Code:
UPDATE user SET homepage = '' WHERE homepage <> ''
Note in all cases those are two single quotes next to each other '' not a single double-quote character.