taghaboy on "some code base64_decode and files in my website?"

hi all,
I have some strange files in my website, and i dont know how it was her, for example i have in the root and in the folder "www" a php file :
default.php
with this code inside it :
<?php eval(gzinflate(base64_decode(".......; ?>

hacking code removed by moderator

Also i have some code in .htaccess with a link inside it :
beritshalom.org/hmod.html

Is any one know how those files are inserted in my website?

Thanks