I just setup my second customer.

I was testing their ftp access and noticed that it is possible to access the directory tree above their home directory!

For example, when they ftp in, they are at /var/www/vhosts/their.site.com/. From here they have access to their httpdocs directory as expected. Unbelievably, they are able to cd .. up one level to /var/www/vhosts. From there, they are free to move around to other customer sites. How can that be?

What do I need to do to clamp this down so that my customers can't see other customer's directories? This is very bad and shouldn't be the default behavior.
Thanks
George