A better question would be "How did piggybacking a tradeline work?"

This was a simple yet effective way for someone to give their credit score a very quick jolt.

It works like this:

Step 1 - Find someone who has absolute trust in you, i.e. your mother, father, best friend, girlfriend, boyfriend etc.

Step 2 - Make sure this person has excellent credit

Step 3 - Have this person call up one of the credit card companies in which they have an account and add you as an authorized user

Once this is done, whichever credit card they have added you to will now show on your credit history. The entire history of this particular tradeline will now factor into your credit score. Piggybacking a single card can add 20 or more points to a score overnight.

This was a very popular method used by mortgage brokers for years, but given that the person inheriting the tradeline didn't actually earn this bit of positive credit, the 3 repositories are working to close this loophole.

Experian claims to have come up with a solution that will disallow piggybacking, with Transunion and Equifax apparently following suit in 2008.

Piggybacking tradelines had become an industry in and of itself with companies like Tradeline Solutions allowing people to pay to piggyback a tradeline.