This happens when either your workstation or another workstation that a developer is using containing FTP passwords and other sensitive information has been leaked.
What we recommend you do in order to correct this issue is the following:
1) Download Avast located at http://www.avast.com/free-antivirus-download
2) Install this on all systems that have development access to your websites and do a full system scan.
3) Once you have done this and verified that your systems are clean you will need to change your FTP password and we recommend changing all password related to your Sectorlink account.
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5) You will also want to make sure that there are no other files within your website that have been uploaded that should not be there.
We recommend using AVAST because it is free and will detect and remove this virus.