Back doors are very hard to trace, as an intruder will often create
several avenues into a network to be exploited later. The only real
way to be sure these avenues are closed after an attack is to restore
the operating system from the original media, apply the patches,
and restore all data and applications.
* social engineering is a technique used to manipulate users into revealing information like passwords.
* Answer "Undocumented instructions used by programmers to debug
applications"refers to a trap door, which are undocumented hooks into an application to assist programmers with debugging. Although intended innocently, these can be exploited by intruders.
* "Monitoring programs implemented on dummy applications to lure
intruders" is a honey pot or padded cell.
A honey pot uses a dummy server with bogus applications as a
decoy for intruders. Source: Fighting Computer Crime by Donn B.
Parker (Wiley, 1998).