I have had a couple of occasions where I found log entries like this :
2007-09-21 00:46:25 W3SVC849604990 PE2650 216.242.142.233 GET
/shopcontent.asp
type=%3ca+href%3d%22http%3a%2f%2fk2njydpenispumpgaga%2einfo%2fpenis%2benlargement%2bpill%2fpenis%2benlargement%2bpill%2btestimonys%2ehtm%22%3epenis+enlargement+pill%3c%2fa%3e
80 - 74.6.28.233 HTTP/1.0
Mozilla/5.0+(compatible;+Yahoo!+Slurp;+http://help.yahoo.com/help/us/ysearch/slurp) - - www.cobbq.com 200 0 0 16159 370 2264
They appear to be from Yahoo's web crawler but are obviously attempting to
hack or spam my server.
I have blocked all 74.6.x.x IPs for now, until I can figure this out.
any ideas