Spammers seem to be working a little bit harder these days, according to Symantec, which reported Tuesday that unsolicited e-mail made up 90.4 percent of messages on corporate networks last month. That represents a 5.1 percent increase over last month's numbers, but it's nothing out of the ordinary. For years, spam has made up somewhere between 80 percent and 95 percent of all e-mail on the Internet.
Symantec reported that nearly 58 percent of spam is now coming from so-called botnets --networks of hacked computers that can be misused by criminals to steal financial information, launch attacks or send spam. The worst of the spamming botnets -- called Donbot -- generates 18.2 percent of all spam, according to Symantec.
These botnet computers can be rented out on the black market by anybody, but in recent months some spammers have been moving away from botnets, experimenting with a new way to sneak their unwanted e-mail past corporate filters, according to Adam O'Donnell, a researcher with antispam vendor Cloudmark.