...what shall I do to remove the harmful code ???
1.) Do not longer login on your FTP or Web Interface
2.) Check with a Powerfull Antivirus Program your Home PC .
(There is very Important, the most Trojaner on the websites come from own PC per FTP.)3.) If your Sytem clean change all your FTP and SQL passwords.
4.) Do not call your website
5.) Login on your FTP and remove the Code, check all your *.php and *html files on your FTP server.
6.) Have you all this done, call your website and check with the Online Antivirus Program your website.
Edit: it does not matter whether virus or trojan
mfg Andi