What is wardialing?

"War dialing, also called scanning, is dialing a large number of telephone numbers in the hope of finding anything interesting. Interesting items often include test tones, computers, Voice Mail Boxes (VMB's), Private Branch Exchanges (PBX's), and government offices.

A common technique is to find one telephone number owned by a target and then to war dial the entire prefix which that number belongs to. For example, if your target is the Chinese embassy in Washington, D.C., you would dial every number starting with (202)328. That's ten thousand numbers.

War dialing one telephone number takes approximately 35 seconds. This means that war dialing a prefix of ten thousand numbers will take just over four days.

In general, people do not like to be called. To be as polite as possible while war dialing, try to war dial business areas at night, when very few people are at the office. Conversely, it is best to war dial residential areas during the day when most people are at work and few people are asleep."
What is wardialing?