Those addresses are starting to land in spam recipient lists. Botnets are starting to send thousands of messages to those addresses that are never seen by a human, but have to be dealt with by a machine. But then the mailing list server will send thousands of acknowledgments or error messages to the unwitting subscriber.
Patch your Windows machines, people. Use firewalls. Don't let them be taken over and used without your permission. And when you're not using them, hibernate or shut them down, to limit their exposure and limit the amount of time they might be misbehaving if infected.