Steve Ballmer, Microsoft's chief executive, may well have thought that he had landed a knock-out blow with his opening takeover offer for Yahoo, putting an initial 62 per cent premium on the struggling internet company.

If so, then the letter that lands on his desk today will make him think again. Yahoo has decided to fight - though whether it is fighting for its own independence, or just to get a higher price out of Microsoft, was a matter of debate among onlookers over the weekend.