And such a routine, of course, would leave security wide open to anyone who found the trapdoor. The obvious protection here, assuming the situation ever arises, is simply an ethical manufactorer that checks its software thoroughly before releasing it. A trapdoor is a set of special instructions embedded in the large program that is the operating system of a computer. Although they may sound sinister, trapdoors were not invented by hackers, although existing ones are certainly used by hackers who find out about them. The first version requires that the hacker have an account on the system in question.
Many people use call forwarding by special arrangement with the phone company.
When a customer requests call forwarding, the phone company uses its computer to forward all the customers incomeing calls to another number. A call from you to the phone company,some special settings in the phone companys computer, and all calls to your office will ring at your home instead. This little bit of help from the phone company is another tool used by hackers. To understand how this methos works, you have to know something about the way operationg systems work. When a user enters a command, the operating system first places the command in a holding area, a buffer, where it will sit for a few millionths of a second.