Avast is a good free anti-virus but occasionally even the good software makes a mistake. It identified uTorrent as a trojan which deleted the file from the computer. Hopefully this was a mistake on Avast’s part and not part of some larger media monopoly conspiracy.
The beauty though of uTorrent is that it is only 1 file, utorrent.exe, if it gets deleted you can download it again. Version 1.7.7 seems to be the only version identified as a virus so if you’re using an older version or the newer beta version you are safe.