Why is it illegal to watch pirated movies online?

Watching a streamed pirated movie may be illegal because some courts have found that saving a temporary copy of a movie on a computer violates copyright laws, advises FindLaw. Many streaming sites create a temporary copy of the content on the computer or delete the content as it is streamed.

It is unclear whether watching a streamed pirated movie online is illegal, notes Findlaw. Though some courts have concluded the practice is illegal, the U.S. Copyright Office advises that the copies are stored too briefly to constitute a violation. In any event, people who watch pirated movies online are rarely prosecuted because of the difficulty in identifying people watching the streams.