Social Engineering: The Biggest Risk to Internet Security
We rely on security walls to keep intruders out, while leaving gates so that we can get in and out ourselves. Most hacking involves trying to break down or otherwise sneak past these gates, but the easiest way to get in is to convince the gatekeeper to open the door. In networking security circles, this is known as Social Engineering, and it's something you need to know about if you don't want to end up in big, big trouble.
Absolute faith in a security system can ultimately be its greatest weakness, as people grow accustomed to it and fail to hold up their end of the bargain. Every wall has a gate through which people can walk; conventional hacking involves breaking this gate down. Social engineering is getting the gate keepers to wave you past with a smile on their faces.
Read more about it. (Source: Tom's Networking)