Video - How malicious hackers exploit a buffer overflow
One of the techniques to exploit a buffer overflow in a very nice video
A buffer overflow is an anomaly where a program, while writing data to a buffer, overruns the buffer's boundary and overwrites adjacent memory locations.
As you can imagine this is *not good*. It can only return some kind of error, or even be used for making yourself the all-powerful "root" super-user, and hack the attacked machine in all kind of ways.
Assistant Professor Dr Mike Pound details how it's usually done.