The Wordpress virus that affects your index.php files is part of Antivirus’s scheme to infect other computers to get unsuspecting users to buy their software. As soon as you get infected by this virus, if you ever try to upload files to your wordpress installation it will rewrite a piece of code to the bottom of all your index.php files found in the main folder of any wordpress installation as well as the /admin/ folder.
After your wordpress blog has been affected, it infects any users who visit your blog. The cycle goes on and on.
One of the easiest ways to stop this virus is to first change all your ftp passwords, and then remove the code from the bottom of any index.php file. To be even more safe, what I have done is disable writing to the index.php files for any user including myself. This way nothing can write to these files, keeping the virus away. Sure this isn’t the 100% best solution for getting rid of the virus, which is probably still on the server, but it works.
Having a virus on your site will turn off users as their anti virus will alert them that your site is an attack site.
Why is this an internet mafia? You pay for protection that they themselves inflicted on your pc in the first place. They infect you and you pay them to get rid of it.