The report claims that Ballmer and co owe the Danish Treasury a total of 5.8 billion kroner, a hangover from the 2002 acquisition of Danish financial software company Navision. The OS giant sold rights to some of Navision's software to it Microsoft's Irish subsidiary at a suspiciously low price so that it could transfer valuable assets out of Denmark—where taxes are high.
Now, the Danish Treasury is chasing Microsoft all the way to Redmond to try and claw back billions in taxes and interest. It remains to be seen how successful that will be. More here.