You may want to use a data cleansing tool like ringlead to clean up your database
There are several threads on handling bad data like this, which is a bit different than using RingLead, etc. RingLead and the ilk will have scenarios to do this automatically. But you can definitely setup smart lists to capture the most obvious names or domains like
STARTS WITH [special character]
FIRST NAME CONTAINS [numbers]
There are also threads on stopping spam or empty leads at the form level.
Can you link to those threads (about stopping SPAM at the form level)?