Write a php virus for fun

This is a steps to write a php virus taken from Ben Dechrai talk at linux.conf.au here

Step 1

The boom.php reads all php files and add <?php // FILE INFECTED ?> line to the begining of each file.

Step 2

The boom.php reads itself and copy the virus code and inject it into all php files.

Step 3

The boom.php reads itself and encrypt the encode itself using base64 then injects itselft into all php files.

In all cases the virus infects a file multiple times.

Step 4

Same as step3, but this time it check first for the filename hash in the first line of a php file as a marker of an infected file. If not infected then it add the filename hash to the first line then do as in step3.