Well, of course they are.... makes sense when you understand what a UFO is. A UFO is simply an object that you can't identify & which appears to be flying.
I 'saw a UFO' recently - a group of 3 different coloured lights, close together that hovered above me (high altitude) and then shot off at great speed. However, I think it was very likely a reflection in my contact lenses, or just my eyes playing some other optical trick on me. However, since I couldn't identify exactly what it was then it must, by definition, be a UFO hehe!