Official comment
To recover from an infected file that has been synced you need to stop syncing the file or folder where the infected data is located. Delete the file(s) from the web interface, and then use the option there to "view deleted files" and select them again and issue the "permanently delete" command. Then you can restore syncing of the source and the clean copy of the files will be uploaded. Please contact the support team directly if you need assistance with this, using Report a problem link above.