It appears 2010 has been a cracking year for malware developers. Customised malware is a significant threat to any environment, given the fact that controls that can effectively protect against these attacks are limited and difficult to implement. Anti-virus certainly does not provide much protection against a trojan that has been customised to attack a specific organisation. FUD is a term used in malware circles and referes to "Fully Un-Detectable" by AV.
According to PandaLabs 2010 Annual Report:
"In 2010, have created and distributed one third of all viruses that exist. These means that 34% of all malware ever created has appeared -and been classified by our company- in the last twelve months." [1]