It’s almost half a year since security update 896358 has been released which prevents viewing HTML help (CHM) files from network drives. It should be noted that the file actually can be opened only the containing HTML files don’t get displayed.

Until now it wasn’t really an issue for me as I was always opening help files from local disks. But in the last few weeks I am managing help development at work and with company policy having latest files on file server shares I keep having to copy the files to my local disk before testing and reviewing them which soon gets annoying.

To avoid the repetitive tedious task of copying files around I decided to look more closely into the issue. It turned out that you can set the maximum trusted zone in the registry to avoid the problem. Since I trust the complete local network zone at work I raised the trust level by adding the following to the registry:

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\HTMLHelp\1.x\ItssRestrictions]
"MaxAllowedZone"=dword:00000001

Problem solved.