My Error Logs show quite a few 404 entries. The referer is usually google.gr, google.ee google.com.br etc. Please keep in mind, this is not a case of broken links, renamed or removed files. The files in question never existed on the sites (as far as I know). Also, the sites and the directories that the indexes point to have all robots.txt files with the following: User-agent: * Disallow: / The sites are for private use and are not indexed by SEs. I am aware that bots can ignore the robots.txt files. What concerns me is that the file names usually are something along the lines: ....serial-free.html ....CD-key-changer.html ...something-sex.html and so on. Does anyone have any ideas about what's is going on? How do these end up in google index?
As you mentioned that you have restricted your whole website from search engines. Then it is not possible for some one to search it from there. It might be happen due to some one playing with your website url, might be by some spammers...
do these files appear to be in 777 chmoded folders? Check those folders and see if there is a .htaccess file doing some clever rewriting. I've seen some worms that exhibit the behavior you are describing.