php eval(decode(..)) hack

hi all
i have used joomla1.5 to create a website.
all PHP files by the some particular names a code with eval(base_64_decode(.....some random alphanumeric characters......)) function appended to them in the beginning of the file..
the site strts wrking when i delete this code but everyday(that is the next day ) i find the website unavailable again due to this code..

how can i avoid such a hack to continuously editing my files..

thanks for help in advance..

hi all
i have used joomla1.5 to create a website.
all PHP files by the some particular names a code with eval(base_64_decode(.....some random alphanumeric characters......)) function appended to them in the beginning of the file..
the site strts wrking when i delete this code but everyday(that is the next day ) i find the website unavailable again due to this code..

how can i avoid such a hack to continuously editing my files..

thanks for help in advance..

Why are you evaling a decode
do just do $var = base64_decode('string');

This might help allso check for any cron jobs updating the file you are having problems with Better yet this is an Addon Delete it