Digital Signature of installation files is missing (Advices and Solutions)

Problem statement: Digital Signature of installation files is missing while Installing KSOS in Win 7 

Solution: 

1. Install the Windows updates KB4490628 and KB4474419 (Microsoft have updated the algorithm for signing modules and drivers of third-party applications; but as long as Windows 7 is now obsolete and not supported, the updates must be installed manually):
select Title and Product appropriate for OS version and architecture, press Download and run setup
KB4490628 - https://catalog.update.microsoft.com/search.aspx?q=kb4490628
KB4474419 - https://catalog.update.microsoft.com/search.aspx?q=kb4474419

2. Follow the instruction to update Root Certificates: https://support.kaspersky.com/common/error/other/12489#block7

3. Download, unpack and install (by double-clicking) the certificate "DigiCertTrustedRootG4.crt": https://box.kaspersky.com/f/f3970b1152944888b818/?dl=1

4. Check and fix system errors.
-Open Command Prompt (Administrator) https://support.kaspersky.com/common/windows/14637#block0
-In Command Prompt execute the following commands one by one to check system files:
DISM /Online /Cleanup-Image /ScanHealth
sfc /scannow

5. Go to folder C:\ProgramData\ and delete here (if found) the folder with name “Kaspersky Lab Setup Files" (if there is a file with the same name, delete it as well)

6. Restart the PC

7. Install the Kaspersky product