What steps do I need to take to change the default action on Windows XP and Windows 7 when someone tries to open a CHM file? I want the file extension to be associated with notepad.exe for ALL ...

Help files (.chm), disguised as fax report emails, are the latest trick cybercrooks are using to infect PCs with CryptoWall ransomware.

Brazilian firms are the latest targets in a spam campaign delivering CHM help files hiding links to bank Trojans.

The CHM format is a Microsoft online extension file for accessing documentation and help files, and the compressed HTML format may hold text, images, tables, and links -- when used legitimately.

It is said that it can open files in a wide range of formats, including DjVu, XPS , which is similar to PDF, and CHM , which is a Windows help file, so I actually tried using it to see what kind ...

Just delete the CHM file from your installation of 7-Zip. This will prevent the help menu from opening and just cause any attempts at this to fail.