IE7 (Internet Explorer 7.0) reached its 100 millionth installation on 8 January, according to a Microsoft blog.
The company Microsoft uses to measure browser usage, WebSideStory, has also reported that over 25 percent of all visitors to websites in the US are already using IE7, making it the second most used browser after IE 6.0.
Tony Chor, program manager at Microsoft said: "We expect these numbers to continue to rise as we complete our final localised versions." Further installations are also expected following the consumer release of Windows Vista at the end of January.
Separate global browser statistics from TheCounter show that from the beginning of January 64 percent of internet-connected PCs used IE 6.0 and 19 percent used IE7. Firefox came third with 11 percent.