One simple solution I have found is to periodically change the name of the the file or the page.

For example, the form I am using requires the following file to POST the form.

my-site.com.cgi-bin/contact.pl

Simply change the file name to, and the corresponding value on the form itself

my-site.com.cgi-bin/contact2.pl

This takes litterally less than 2 minutes and will eliminate those spam postings, usually for a month or two. When you start to get them again, change the file name again.

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