Attack of the spam

Hello, I have started to notice that my stats showing visitors to my site show links that do not exist. The referer is blank. The link, for example is something like the following: /wp-content/uploads/2007/07//filename.html
where filename.html is the name of a file that does not exist anywhere in my /wp-content/uploads/2007/07/ directory. It is also strange that each link contains two ‘//’ after the /07/ directory.

I had noticed that /wp-content/uploads/2007/07/ directory had a chmod of 777. I have changed it to 755 but am still getting a whole heap of these strange ‘visitors’ accessing my site.

I have read previous posts about modifying the .HTACCESS file, but I’m not sure if this will resolve the problem that I am having, as the referrer to the site is blank.

Any help would be greatly appreciated.