Hi,
Many SEO companies have recently started creating multiple websites for promotion of a single website. They host all these SEO websites on different Class C IPs and add backlinks in those websites which point to the main website of their customer.
We host many such websites for SEO companies. They signup for multiple
shared hosting plans and ask us to setup those websites on different shared servers we have. This helps them to improve rankings of their client's websites. This concept has worked well so far and google has found no solution to differentiate between such addon websites.