I have a website based on Joomla 2.5. Recently people with AVG anti-virus started to complain that some strange windows appear when they open the site. An unknown line of code with comments "Google search bot" appears in index.php files and the permissions set changes.
AVG detected Blackhole and Sweet orange exploit kits. I removed manually all the code but a day later it appeared again. I installed OSE anti-virus plugin and RS Firewall plugin for Joomla and scanned and it said it was OK.Is it necessary to reinstall Joomla? Please, help me. Thank you in advance. Oh, I forgot to say that I can not change the FTP password.