Unblock CHM Files
Attachment Manager Since Windows XP Service Pack 2 (SP2)
Description
Attachment Manager is a new feature included in Windows XP SP2 and Windows Vista intended to stop users from opening malicious files downloaded from the Internet. It does that by attaching a small piece of additional information called zone information to the files, containing the URL from which the file was downloaded. This additional information tells Windows that those files are potentially dangerous.
How does it affect your files
If you download a file from the Internet, that file will be marked as unsafe until you unblock it. When a file is marked as unsafe, Windows might not allow you to open this file, however the exact behaviour depends on the type of the file. This is somehow confusing and might lead to hard-to-find and obscure problems later on. It is therefore necessary to always unblock any file that you trust to avoid any unnecessary problems.
Downloading a ZIP file from the Internet
If you downloaded a ZIP file from the Internet, it will be marked as unsafe. When you extract the files inside the ZIP file using Windows Explorer, it will mark all those files as unsafe as well. It is therefore very important to 'unblock' the ZIP file before you extract the contents.
How to unblock files downloaded from the Internet or just deemed unsafe by Microft such as CHM, Exe, Files
You can check if a file is marked as unsafe from the properties screen (Windows Explorer, right-click, choose Properties).

Click on the 'Unblock' button to tell Windows to remove the 'unsafe' marker.
FAT/FAT32 volumes are not affected.
Attachment Manager is unable to mark files that are stored on FAT/FAT32 volumes. Only NTFS volumes are affected.
If you do not have an Unblock on Right Click option.......... then you have to Disable The Attachment Manager by Enabling.
Disabling the Attachment Manager
The Attachment Manager can be disabled.
The steps to do that are outlined below:
On pressing on the start menu, write Group in the search bar and then select Edit group policy, as shown above.
When the 'Local Group Policy Edtor' opens, come down to User Configuration and select Administrative Templates on the botton left hand side.
On the right hand side, double click on the Windows Components section..
Then again on the right hand side, double click on the second option 'Attachment Manager'
Then come down to the third option right hand side 'Do not preserve zone information in file attachments'
Now right click and select the 'Edit' Option
As you can see above, It is not configured meaning, it is active...........
Select 'Enabled' (Enabled would mean that 'Do not preserve zone information in file attachments' is enabled, which in effect will stop Windows from storing the zone information in file attachments). And then click OK to close the dialog box.
Then to exit the 'Local Group Policy Edtor' just click on the top right hand side X to exit.
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