Never encountered one but I do believe that there are probably bad things out there. There are also, like said before, a zillion things out there that we won't understand until we pass. Electro Magnetic thingies, you know... stuff.
I have known lots of people with stories that do believe 100%. One girl in particular wet her pants on a haunted tour of an old Hotel/Spa/Former Hospital. Every time we walked through the halls we had to crawl through groups sitting down listening to stories and tales of the former inhabitants. So DH and I frustrated with the commotion one night sat in our room waiting for them to stop next to our door. AGAIN they stopped right outside and started in with their tale. We waited until they all sat, one sat leaning AGAINST our door... AND THEN WE TACKLED IT! SLAMMING AND MOANING AND SCREAMING at the top of our lungs... The girl sitting there wet her pants, she left quite the puddle. LOL!