FreeFixer uses cryptographic hash functions to convert file contents into a small piece of data which uniquely identifies a file.
Let's say you click on a file in the scan result called GoogleToolbarNotifier.exe. Since there are many different versions of this file   the freefixer.com web site needs to know exactly which file you clicked. The FreeFixer program does not want to send the complete 69KB file data to the freefixer.com web site to uniquely identify GoogleToolbarNotifier.exe. Instead the FreeFixer program sends the hash of the file, which is much smaller. For example, the SHA-256 hash which FreeFixer is using is only 32 bytes.