Why do mosquitoes 'choose' to bite some people more than others?

There is much anecdotal evidence that mosquitoes bite some people more than others. In recent years, scientists have proven scientifically that this phenomenon does actually exist and that it is likely to be mediated by differences in body odours. However, investigations have merely scratched the surface in their attempts to explain the chemical basis for differential attraction - until now. It might be logical to assume that if you are bitten less by mosquitoes, your body produces less in the way of attractants. But, recent evidence may have turned this theory on its head, suggesting that being 'unattractive' to mosquitoes is caused by an 'in-built defence system' of naturally produced compounds that interfere with the way they find their human hosts.