All messages sent over corporate networks are spam, or almost all

According to a report of Symantec Corp.'s MessageLabs Intelligence unit unsolicited e mail
 accounted for 90.4% of all messages received on corporate networks during April, an increase of 5.1% from a month earlier.

In addition to using botnets spammers in recent months have been experimenting with a new way to sneak unwanted e mail past corporate filters.

Adam O Donnel a provider of antispam tools also added that often a spammer will rent legitimate network services and then blast a large amount of spam at the network of a specific ISP. The idea is to push as many messages as possible onto the network before any kind of filtering software detects the incident.

Security experts note that social-networking spam can't be filtered at the corporate firewall and appears to come from friends of the recipients.