I've no idea if their service actually works but if it does, it's illegal in the EU and it would also be illegal for their clients to use such information to e-mail those visitors.
EDIT: talking about relead.com mentioned in a g+ reply.
EDIT: talking about relead.com mentioned in a g+ reply.
As I read their pitch, they identify the company a visitor to your site represents, and then they suggest the contacts at that company and give you a bunch of info about the company and the key staff.
"Unmatched in quality and accuracy We can track exactly WHO is visiting your website, and how valuable or interested they are in your business"
"See complete company profiles of your visitors: Company Name, Industry, Size. We'll also be adding Credit Risk soon."