Microsoft's decision late last year to switch on "silent" upgrades for Internet Explorer (IE) has moved some Windows users to newer versions, but has had little, if any, impact on the oldest editions, IE6 and IE7, according to usage statistics.

In December 2011, Microsoft announced it would start automatically upgrading IE so that users ran the newest version suitable for their copy of Windows.

Under the plan, Windows XP users still on IE6 or IE7 would be updated to IE8, while Windows Vista or Windows 7 users running IE7 or IE8 would be pushed to IE9.

Previously, Microsoft has always asked users for their permission before upgrading IE from one version to the next, even if Windows' automatic updates was enabled.

First to get the automatic treatment, Microsoft said, would be Australia and Brazil, both guinea pigs for the January 2012 debut. The program would then be gradually expanded to other markets.

Yesterday, Microsoft declined to disclose what other countries, if any, had had the auto-upgrade switched on.

But in Australia and Brazil, the move shuffled share among some editions of IE, according to data from StatCounter, an Irish Web analytics company that publishes country-by-country usage share numbers for IE6, IE7, IE8 and IE9.

In both countries, IE9 jumped unexpectedly in February, the first full month after the auto-upgrade switch was thrown, while IE8 saw an almost-corresponding decline in share.