In the same way that a snowshoe spreads the load of the wearer across the snow, snowshoe spam spreads around the world using many IP addresses to send spam. Spammers send millions of spam from rented or compromised IP addresses until they are detected and shut down. Spreading across the world, sending from many IP addresses makes the spam more difficult to detect by spam IP reputation filters.
Often legitimate companies are tricked into purchasing lists of e-mail addresses that are advertised as having opted in to marketing. These marketers are sending snowshoe spam to illegally obtained e-mail addresses on behalf of some legitimate companies. Some snowshoe spam is spoofed to look as though it is valid, but is leading recipients to phishing sites and voicemail boxes that have been set up to acquire information from them.
This technique is fairly new, cropping up in the last couple of years. Due to effectiveness and lack of action by law enforcement agencies it is expected that use of this technique will continue to increase.
The IP addresses or even subnets of IP's can end up blacklisted after being compromised.
McAfee SaaS Email Protection’s Stacked Classification Framework protects our customers from spam threats by filtering based on statistics, heuristics and reputation, and includes McAfee Global Threat Intelligence message reputation, which all work together to better protect businesses from the threat of this and other types of spam.