BC! is a file extension mainly used by a direct network file exchange (P2P) program called BitComet. BC! File it is generated when the user starts downloading the file. It stores data of downloaded files until the download operation is interrupted and the end of the file is not reached. This can happen, for example, because the computer needs to be turned off. You can continue downloading this incomplete file at a later time.

BitComet is software developed by BitComet.com and uses the BitTorrent protocol for file exchange.