The April, 2008 market share data has some significant variations from established trends.  The following major anomalies occurred on April 18th:

A 25% increase in visitors

A 3% drop in Firefox share

A 4.9% increase in Internet Explorer 6.0 share

A 3.4% increase in Windows XP share (with a small drop in Mac share)

A .7% drop in Windows Vista share

Since April 18th, all trends have returned to expected values, including an expected uptick in Vista share due to the release of SP1.

Once we discovered the extent of the variations, we have worked diligently to discover the cause.  The variations were coincidental to the release of Vista SP1 to automatic updates, so we initially thought there might be a connection.  However, our investigation showed Vista SP1 had nothing to do with the problem.

What happened was a distributed collection of sites inadvertently caused the problem.  We can't identity the sites responsible, but the nature of the problem is that all the millions of new visitors we saw were part of a massive marketing campaign that only worked on Internet Explorer.  Since the campaign only ran on Internet Explorer, it caused respective drops in Firefox, Safari and Opera share.  Also, operating systems that do not have significant Internet Explorer share were impacted, especially the Mac.

As of 6am on May 7th, the skewing data has been removed.