untypical or atypical?

Am I right in thinking that 'untypical' and 'atypical' mean exactly
the same thing? Which word is preferable nowadays?

I was (probably wrongly) under the impression that there was no such
word as 'untypical'... until yesterday when I heard a BBC news
presenter use it. Referring to my dictionary, I was surprised to find
it listed.

I think 'untypical' sounds more explicit that 'atypical'. However,
'atypical' turns up vastly more Google hits than 'untypical'. Am I
right in thinking that 'untypical' was, at one time, not considered a
word, but it has now been uttered so many times that it has now become
universally acceptable?

If so, I'm glad.