Are you able to login via FTP?
If you are, then you should be able to delete the offending page and replace it with a temporary notice.
If you aren't able to login via FTP, then you'll need to contact his provider ASAP to reset the passwords. It's worth reporting the break-in to them anyway.
iMac 27" 3.4GHz Core i7, 20GB RAM, 256GB SSD • 27" LED Cinema Display
MacBook Pro 13" 2.8GHz Core i7, 16GB RAM, 128GB SSD