We should all know by now that the fingerprint biometric is a bad one: not only can you duplicate it fairly easily using just gummy bears, or increase the risk of having your finger cut off for you, they also give too many false negatives; some people will never be able to use fingerprint scanners.
The problem here is that because they have to automate the fingerprinting process, you get a lower level of accuracy in the scans. No two prints by the same finger are ever exactly the same. This is corrected for by error correction codes, which adds information to the prints to allow the computer to correct for these disparities. If you can get to these codes, you can find out information about the original fingerprint and the amount of data loss that is expected. So searching through the error correction code database allows you to find a fingerprint that is similar to yours and has a large correction. This means you can become this other person fairly easily.