Here is a stumper. I would have seen this movie on TV sometime between 1977 and 1980. It was on our local PBS station late night. My brother and I were allowed to stay up and watch Monty Python, and he came on PBS at around 11:30. This was either on right after it or in place of it one evening.
The movie, and I don't know if it was a full length movie or just an hour-long show, was about a teenage girl who began receiving scrambled broadcasts over her computer. Eventually it cleared up and it was a dark haired teenage boy who was talking to her. She fell for him and made plans to be with him. Her brother tried to stop her.
At the end it was revealed that the boy was an alien and he had either trapped her on his planet or trapped her in the computer.