I want to reject any URL request that contains
the character string "252Esystem". My goal is
to block all these hack attempts on my phpBBs,
since all they do is suck up bandwidth. I have
not had any luck getting my Apache to fail them.

RewriteEngine on
RewriteRule (.*)252Esystem(.*) - [F]

I tried a couple variations of this syntax, and
I have not come up with anything that has worked.

PS- I do Rewrites based on referrals already, so
my Apache server should not need any new modules.

Thanks,
Scott