Dianne, that sounds like it might be a superstitious or cultural belief, rather than a metaphysical observation.

In fact, "spirit" (ie loved ones who have passed or and/or guides/angels) will communicate in a number of ways - depending on how the person they are communicating with are able to receive the energetic transmission - for some it will be words and sentences, but more often people perceive sensations, images, scents or just a sense of sudden understanding of what is meant. If a spirit were to have malevolent intent, it's quite apparent in the same way as if you meet a living breathing person who has malevolent intent - your intuition lets you know loud and clear. It is always a good idea to say a prayer and/or surround yourself in white light whenever you encounter spirit, keep yourself protected while you ascertain who/what you are dealing with.

HTH