A BC! file refers to a partially download torrent that has been created using the BitComet BitTorrent downloader.
These files are created by the downloader as soon as the torrent download begins. Once the download finished, the BC! file extension is removed and replaced with the file extension of whatever file has been downloaded.
.bc File Extension
Developer:
BitComet
什么是 bc 档案以及打开它的方法 - BitComet Incomplete File
开发商:
BitComet