Don't re-download. PAR files are used to fix bad rars. Google QUICKPAR and install the app, it will fix the rars using the PAR files. They are used with bigger
downloads to avoid the hastle of having to re-download should you have a few bad files. It is very common to see them with 360 isos, movies etc.
Parchive | Parchive (or parity volume set archive) is a forward error correction-style system that can be applied to one or more files to allow recovery when data is lost or corrupted. When used with collections of files, some missing files can be regenerated. @
http://en.wikipedia.org/wiki/Parchive