Our .CHM Files Don't Work Anymore. Why?
http://www.helpscribe.com/2008/01/our-chm-files-dont-work-anymore-why.html

HelpScribe
2008

Abstract:

If you are delivering your help from a network location and you notice that .CHM files don't work anymore, don't be surprised. Recent Microsoft updates include tighter security for .CHM files. After installing the updates you can no longer run .CHM files from a network location. However, you can still run a .CHM file on your local machine.