Symantec reported this week that unsolicited email, junk mail or spam to you and I, made up 90.4% of all email on corporate networks last month.

It appears spammers are working a little bit harder in order to get their messages past corporate spam filters. They report that almost 58% of spam is coming from botnets, networks of hacked computers. The worst of these is one called Donbot that accounts for just over 18% of all spam. These botnets are rented out to spammers on the black market. But recently spammers have been moving away from botnets and have started renting legitimate network services, mostly in Eastern European countries such as Romania.
Using these networks they blast a huge quantity of spam at one ISP’s network in the hope of pushing as much junk mail as possible onto the network before any kind of filtering software detects it.
Social networks are also increasingly being used and in the past week both Facebook and Twitter users have been targeted with phishing attacks designed to steal users passwords. The hacked accounts are then used to push out spam to the victims friends on the networks.
Social networking spam is very difficult to filter at the corporate level and appears to come from a friend of the recipient. It is therefore very effective from the spammers perspective.
Symantec’s report can be found here