Use of this is frowned upon by several parties. It may not only be avast, but due to existing P2P-threats.
As for why Malwarebytes blocked QBitTorrent, this is because QBitTorrent, and all Bittorrent software, are what are known as Peer-to-Peer (P2P) applications meaning it connects to many different servers/IP addresses (this is how files are downloaded through QBitTorrent) and because of this, sometimes QBitTorrent will connect to a server that is also known for hosting malicious content.
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