Unfortunately .CHM files can harbor viruses and so
Microsoft decided to impose new rules on .CHM files in their latest Service Pack
2 (SP2) for Windows XP. If you are running a version of Windows older than
Windows XP SP2 you can ignore the rest of this paragraph: my .CHM files will
display for you without problems. But if you are running Windows XP SP2 then it
is important that you elect to Save the .CHM file to your hard drive rather than
Opening it directly from my web site. This is important because once the .CHM
file is on your computer you need to right-click on its filename and then select
Properties. At the bottom of the Properties page you may notice a Security
warning that says "This file came from another computer and might be blocked to
help protect this computer".
Click on the Unblock button and you will then be
able to read the complete textbook. You will know that Windows XP SP2 is
blocking the .CHM file if when you try to view it every page has been replaced
with the message "The page you are looking for is currently unavailable" or "Navigation to the webpage was canceled".
Published: February 28, 2010