.!QB File Extension

Incomplete download file created by qBittorrent, a Torrent client; appends the ".!qB" extension to a file as it's being downloaded, and the extension is removed when the download is complete; similar to .!BT BitTorrent and .!UT uTorrent files.

NOTE: The !QB extension is only used if you check the "Append .!qB extension to incomplete files" option in the Downloads settings (Tools → Options and then select Downloads). The option is unchecked by default.