One of the major pillars of anti-spam filtering, the blacklist, is rapidly losing effectiveness, according to ZDNet. In the last few weeks spam has been spiking because spammers are sending unsolicited commercial emails not so much through infected zombie computers, but rather through those computers' major ISPs. When the blacklists start to include domains such as aol.com, msn.com, yahoo.com and all of the other major providers of email and internet service, they become practically useless.