Sorry, should have said more.
The fact you are even asking indicates that you think it is a scam as well.
Almost 100% of these "free" holidays are linked to time shares and holiday clubs.
You will often find the "free" holiday will not really be free, and you will have to pay for flights, or some sort of administration fee.
Or IF it is free they will may it so difficult for you to take it you wont bother (they give you difficult dates or difficult airports to fly from).
SOME people say that have had "free" holdays with these offers (but probably spend 4 hours being sold a time share while they are there).
Personally I would ignore it, but it is up to you.
If you begin to show an interest you will probably regret it(you will also get bothered for ever with similar calls from other companies as your name will be passed on to other organizations if you show an interest)