By definition UFOs do exist .They are flying objects that have not been identified.

Several here have used this definition but I disagree. 'UFO', from the very start, has been a misnomer, though this word will not go away. Several explanations for what can give rise to a perception described or recollected as 'UFO' make use neither of objects nor of flying things.

Venus is the number one suspect (e.g., J. Carter's 'UFO'), an object for sure, but 'flying'??
The play of disco lights on clouds is another suspect, neither objects nor flying.
Entoptic phenomena (very remote suspect) are neither objects nor flying and not even 'out there' in the sense of a disco light.
Real objects can be perceived as flying though they are not (autokinetic movement, which can happen if you see a tiny object in front of a big background without stable frame of reference close by, like the sky is; what moves there are your eyes).

That's in short why I consider the use of the above definition as wrong for it excludes some possible explanations.

There are many more possible explanation, all well know. One of many is that there are actually alien crafts visiting us, and I find it very amusing that some people consider others lacking the open mind when all they themselves entertain is one particular of many possible explanations.

LH, the juxtaposition of the two words definitely appeared is priceless.

Whats the difference between those that believe in God and those that believe in UFO's? (dianavan).

That's an interesting question. On an empirical level, these two groups have not much in common. If there is any correlation at all, it is negative; that is (traditional) religious people are even less likely to believe in UFOs than non-religious. (Trad.) Religious based beliefs are negatively related to degree of education, non-religious-based beliefs are unrelated to degree of education, to name just one of many more differences.

I would have loved to cite Massimo Pigliucci here for one obvious similarity, but I do not refind the quote so you have to make do with my clumsy retelling:

For both, the object (object? focus) of their reveration, attention, curiosity is extremely and suspiciously elusive. Both an omnipotent god and (from our present narrow point of view) near-omnipotent alien civilisation visiting that often that roughly 20% of North-Americans report having seen a UFO, could easily demonstrate their power in a way that no further doubt would be possible. Curious that they don't.

As others, I consider it nearly sure that life exists outside of this planet, fairly likely that even intelligent life exists outside of our planet (though not necessarily at the same time), very unlikely that we have been visited even once in time. As for the near continuous (epidemic in the North Americas of the last 50 years) reports of UFOs, I consider them a sure sign of intelligence at work, but not of alien origin. The intelligence at work here is the intelligence between the two ears of the human species.

Wolfgang