While worms and viruses typically attack indiscriminately and self-propagate to any machine available, today's sharper threats go after specific companies or users with a specific objective. Their goal: to gain information or simply to extort money.

The threats are being carried by email, attachments, various files stored on media such as CD-ROMs, DVDs or flash drives. Once the devices are attached, victims unwittingly download the Trojans or spyware into their networks.

Fewer machines, more danger

"We are seeing more specific targeted attacks," said Vincent Gulloto, vice president at AVERT (Anti-Virus Emergency Response Team), McAfee.

He noted criminals now engage in direct stealing and extortion, either by encrypting confidential documents then demanding money in exchange for unencryption, or threatening firms with denial of service (DoS) attacks.