Story here, in Wired.
But it took almost two years for anybody to catch on. Thanx is due to CalTech grad student Virgil Griffith, who built the Wikipedia scanner to track this kind of edits via their originating IP.
Of course, it occurs to me that this could still be done undetected – an exec would just have to make the desired edits from an anonymous terminal at a public library or cybercafe.
The endless struggle between defensive and offensive capabilities continues.