Infection relies heavily on hiding from and evading traditional security solutions. Targeted attacks will often develop new and unique malware that is customized specifically for the target network. This technique allows the attacker to send in malware knowing that it is unlikely to be detected by traditional antivirus tools.
Another common way to avoid security is to infect the user over a connection that security can’t see into, such as an encrypted channel. Attack transmissions are often obscured in SSL-encrypted (Secure Sockets Layer) traffic or other proprietary encryption used in P2P (peer-to-peer) networking applications and IM (instant messaging), for example.