If you are being met with an invalid signature error while trying to update your iTunes, here is a simple tip to navigate around the error message and proceed with the installation.
How To Fix the Invalid Signature Error in iTunes
Following receipt of the error message, reboot your router, and temporarily disable your antivirus software and firewall. Once this is done, try to download the Apple Software Update again.
To do this, simply open iTunes, click on the Help menu > Check for Updates.
If the problem persists, the only solution is to download the iTunes setup (.exe) directly from the Apple website. You should then attempt to do a clean installation and/or update.
