"So what's driving the spammers then? According to Google, it's partially due to the failure of spam-detection vendors.
""Whenever we see an unusual spike it's not always the case that spammers have increased their volume arbitrarily," Raghavan argued. "It is the case that a few vendors have been ineffective at detecting the links. Once spammers figure that someone is not detecting their technique really well, they pummel the system.""
