PHP embedded in GIF files

There is a security flaw in GIF files that allows a PHP program to be inserted into the GIF file. The way this works is the file has the proper GIF89 headers to make it a valid file (thus not caught by a PHP upload script), but yet the PHP code is embedded. A hacker can use it to find out passwords, etc, since the .php code would run as the webhost.

I never knew this was possible until I read about it when someone tried it on our server.

This site has what you can do about it...
http://www.phpclasses.org/blog/post...GIF-images.html

I saw many times that when I loaded a page (page.php) I was redirected to a 1px gif page. What that the "hackers" pages? If so, how could I protect myself from this kind of hack?

It's hard to say from your description what their intent was. It could be anything from a cookie reader, a wrong redirect, a page tracker, or a legitimate purpose. Not sure what you could do to avoid those, except to only go to trusted sites, which I know is not the most practical of advice in the real world.