Originally it referred to an abandoned Web site that remains online (such as a ghost site or an orphan annie).
The definition of "zombie" has been extended to include a PC that has received either a virus or a Trojan program which causes it to be used as a spam generator without the user's knowledge. For example, in June of 2007 a 27-year-old man, Robert Alan Soloway, described as one of the world's most prolific spammers was arrested and federal authorities said computer users across the Web could notice a decrease in the amount of junk e-mail. He was accused of using networks of compromised "zombie" computers to send out millions upon millions of spam e-mails.
The use of PC zombies to generate spam increases as more small businesses and individuals gain Internet connections. Spam is a major problem because it uses up bandwidth and because it can make the Internet experience very frustrating! Zombies are considered a security breach. It is necessary to use
anti-virus software on your machine and run it on a regular basis.
The term zombie also describes a Unix/Linux process that have ended but the process creator/parent has not acknowledged this yet. What happens is the zombie process will consume a small amount of resources until it is killed by the parent process that created it.