After dinner I checked Twitter and saw the following tweet from @marcesher:
It didn't take long for me to track down the cause of this problem. In the Virtual File Explorer code on line 50 of Service.cfc there it was:
writeDump(var=q, output="c:\wtf.html", format="html");
My apologies to anyone who had downloaded and installed Virtual File Explorer. To fix either remove the line in question or download and install again.