Being new here I'm not privy to the members but the exploits shown in the 3 posts appear legit. Although, I have my register globals set to off. Some hosting companies such as hostgator (which is the #1 featured hosting company shown on this site) has register globals on but it can be changed in the cpanel via the Software/Services area > php.ini Quick Config.

If the globals are set to off and this is still taking place then there likely is a vulnerability somewhere in the script, although see more I'm not sure which version you're using. I'm testing the 6.1.5 and it seems stable but I've just started on it, so far, so good :-)