Here is something to remember...................
The iframe attacks from hackers are done by:
Client side PC infected with virus.
Virus gets FTP username/password from the FTP clients.
Using the username/password, the virus downloads the index files, add iframe
code and re-uploads it.
The iframe code points to the same virus. So, anyone accessing this website
gets infected with the same virus, and it uses the FTP username/password to
spread again.
Temporary Solution:
The bandaid fix for such a problem is to change the FTP username/password.
Permanent Solution:
1) Change the password of the infected clients.
2) Before updating the new password in the FTP clients, do a full system Virus
scan with a reliable virus scanner updated with the latest virus definition
files.
3) Do not to save (remember) the FTP username/password on FTP clients.