Critical. Fixing is strongly recommended.
Cause of the problem can be malware.
Kaspersky Internet Security
Kaspersky Total Security
Kaspersky Small Office Security
Files with the .SCR extension are usually screen saver files. If the .SCR files association is damaged, then any attempt to open screen saver files or other files with the .SCR extension can cause a malicious program to launch, which can subsequently be used in order to gain control of your system and your personal data.
After the fix is performed, the .SCR files association will be restored. There are no side effects. The Autocad application also contains scripts with the .SCR extension. After the application is installed, it changes the program associated with the .SCR extension to Notepad. After the fix is performed, the .SCR files will not be associated with the Autocad application and will not be opened only by Notepad. The fix will not impact on the Autocad functioning.
You can roll back to the previous settings.