To celebrate the fifth anniversary of the official UK download chart, the Official Charts Company - the body who compiles the British charts - have published the Top 10 most downloaded tracks of all time.While the top spots are dominated by recent singles from Lady Gaga and The Kings Of Leon, Canadian rockers Nickelback's mammoth 2008 hit, Rockstar, entered the chart at number 10.Digital sales now account for around 98% of the singles market.