How to identify them: They move slowly and eat brains, but rarely display any.
These creatures plod along, day by day, mindlessly copying sensitive data to USB drives or attaching them to email messages, where they are promptly lost, creating a huge security and legal mess for their employers.
This type of zombie isn't malicious, says Tim Matthews, senior director of product marketing for information and identity protection at Symantec. In fact, most of them think they're being helpful by trying to get work done at home or on the road.
"The biggest issue is the well-meaning insider who doesn't understand he's not supposed to email himself sensitive files or copy them to a flash drive," says Matthews. "Or he knows he shouldn't do it but perceives it as a very small risk -- like not wearing a seat belt when going to the store to buy milk. He thinks no one will know or that they won't lose that data, but in many cases it ends up being lost."
The other kind of zombie is one that falls for phishing emails or scareware scams, unwittingly installing malware that can steal data or bring down the network.
"Both of these types of insiders make the wrong choices and go about their days in a trancelike state, oblivious to the security risks they pose to the organization," he says.
Your best defense: While you could cut off their heads, the HR paperwork would be murder. A better fix is to fill their heads with information, so at least they know the rules and the risks, says Matthews.
But because not all zombies can be educated, smart organizations should also implement a data loss prevention solution that blocks sensitive information from being attached to an email message, copied to a thumb drive, or uploaded to a cloud storage service, he says. Or the system could allow the data to travel, but only after it's been encrypted.
"Typically, once people know the DLP is in place you see the number of incidents go down, as people start paying closer attention to their own behavior," he adds.
How to identify them: Sallow skin, bloodshot eyes from staring at screens, often seen holding iPhones.
They may be bringing their own devices to work or keeping their YouTube addiction to lunch hours, but these fiends are still feasting on your bandwidth, draining the lifeblood from your network.
The BYOD revolution in particular has caused a strain on network bandwidth, especially as more business-critical apps are delivered via the cloud, says Jim Melvin, CEO of AppNeta, a provider of cloud-based performance management and end-user experience monitoring services.
"These vampires are everywhere," he says. "Some are updating iTunes or streaming Pandora Radio, others are playing games or updating Facebook. The really scary ones are downloading media files and installing viruses. Not only are these people not doing their jobs, they're also slowing everyone else down. Then suddenly your IP phones stop working because somebody is downloading a BitTorrent."