kevin8

I managed to delete it via ssh with Putty, following the instructions here:

Solution: Delete plugin via Secure Shell (SSH)

Your plugin might had uploaded some hidden/nested files inside the plugin directory which didn’t appear in FTP.

If you have SSH access to your blog,

Login your site via SSH.
Use SSH commands to nagivate "../wp-content/plugins/".
Use ls -al to see the full list of folders.

Delete the particular plugin folder with rm (Folder Name).