Allowing software with invalid signature to run or install
Some software from the web comes with an invalid signature, and it is by default programmed in Internet Explorer, Microsoft's web browser, to stop installing and running in the Windows operating system. This is a security action that prevents software with an invalid signature from installing or running. This is because it could be a security threat and harm your PC with a virus. Sometimes you may need to allow or prevent such software. In this case you have to edit the internet options in Internet Explorer. In security options, select 'Allow software even if signature is invalid' in order to be able to run or install the software. If you want to prevent the software, deselect the option from the check box.
For your operating system to allow software with invalid signatures to run or install, you need to change some settings in the internet options.