banks generally record bank credits from other banks and business' to generate an internal credit profile which is used to offer loans, credit cards, overdrafts etc etc
you can easily manipulate banks credits through online banking ;p
faster payment 1000 from bank A to bank B then back to bank A, repeat 3 times in a month, bank thinks you have a salary of 3k per month.
next time you want to have a credit card, (assuming you dont gave bad credit to begin with) you shouldn't have a problem,. thus the road to good credit begins