In order to install Bitdefender Security on systems with Windows 7 Service Pack 1, several Microsoft Knowledge Base packages need to be present on the device.
You can install them via Windows update, or you can manually install those specific packages.
Install using Windows Update
Press the Windows Start 
button, select All programs, go to Windows Update and Check for updates.
Make sure your device is updated.
Manual install
For x86-based systems
- Download and install KB4490628 – https://catalog.s.download.windowsupdate.com/c/msdownload/update/software/secu/2019/03/windows6.1-kb4490628-x86_3cdb3df55b9cd7ef7fcb24fc4e237ea287ad0992.msu
- Download and install KB4474419 – https://catalog.s.download.windowsupdate.com/c/msdownload/update/software/secu/2019/09/windows6.1-kb4474419-v3-x86_0f687d50402790f340087c576886501b3223bec6.msu
For x64-based systems
- Download and install KB4490628 – https://catalog.s.download.windowsupdate.com/c/msdownload/update/software/secu/2019/03/windows6.1-kb4490628-x64_d3de52d6987f7c8bdc2c015dca69eac96047c76e.msu
- Download and install KB4474419 – https://catalog.s.download.windowsupdate.com/c/msdownload/update/software/secu/2019/09/windows6.1-kb4474419-v3-x64_b5614c6cea5cb4e198717789633dca16308ef79c.msu