We had a network of sites, and they all looked the exact same to the user, but to google, each site had a completely different structure, and it kept the network safe for years before a google employee (or we assumed google employee - @google.com email) signed up for the service without us knowing, and discovered the entire network by placing a large order which gave him links across the entire network. Within 1 week of them signing up, our entire network of 10k domains was dead, and everything they linked to was delisted from google. We had to shut down the network, and refund all unused credits from our customers.