Hackers Attack

I bought a hot joomla event template and a hot joomla business template sometime ago. I however have been getting the some one hack into the sites changing the index.php files in the hotjoomla templates of the sites and re directing to some other malicious sites. I have changes all passwords and even got a SiteLock security to monitor the site and yet issue still comes up at least once a month in the last few months. Please what is the problem with these templates?

Change CHMOD form cpanel's file manager or install xEplorer RC5 to forbid writing to 644

Thanks, but do you mean I should change file permission or chmod the file to 644?

Chmod is permission (unix) if you use IIS then forbid file write for all except administrative accounts not including IIS site execution account.