Have a read of this, please be safe....
Torrents and torrent-based Apps and Add-ons like Popcorn Time P2P Plexux etc are where the sketchiness comes into play.
When you download from a torrent, you're unknowingly also complicit in a process called reseeding;
basically meaning your computer is being used as a server to share the file with other users as you download.
At that point, you are no longer just passively watching the video, but are participating in the distribution of this file.
It is also very easy for other torrenters to unmask your IP address since you're acting as a public server, copyright holders will often uncover the identities of pirates this way.
Depending on the level of participation, fines of anything from £300 – £3000 are known to be given out regularly.