There are PC viruses that captures FTP login details while you are using them. They can then connect to your FTP account and change the files on your website, infecting it with malware.
If this has happened to you, take the following steps:
- Using a good antiviral software, scan and clean the PC you use to connect to your site
- After making certain your computer is clean, change your FTP passwords and your Control Panel passwords
- Edit and remove the code from your files. Either reupload the previous non-infected versions of the pages, or look through the code for lines that begin with <iframe and link to other sites
- Ensure that the web software you are using, such as WordPress and Joomla! are all up to date
If you are still not certain if your site has been repaired, please raise a Support Ticket with the Customer Services team.