Same issue here. I am using mod_security to block the user-agent
SecRule REQUEST_HEADERS:User-Agent "Bittorrent" "id:10000002,rev:1,severity:2,log,msg:'Bittorrent Hit Detected'"
I would change the log to nolog after you verify it is working to avoid filling up your log file
SecRule REQUEST_HEADERS:User-Agent "Bittorrent" "id:10000002,rev:1,severity:2,nolog,msg:'Bittorrent Hit Detected'"