I have 9 PC's in my home. 7 are running Win7 64bit and 2 are running Win8.1 32bit. All PC's are running Bitdefender Antivirus Plus 2016. All of the PC's have the latest Win updates from Microsoft and Bitdefender updates. On 1 computer, there is one (and only one) webpage that reports an invalid security certificate. I am having this problem using IE11 and using Chrome. Every time I try to access the webpage for Lionel trains support. Since I'm new on the forum, I can't post the actual link. Let's just say it has "lionelsupport" and "com." On this PC using IE11, I get a message "There is a problem with this website's security certificate." If I continue to the website and display certificate info, the certificate issuer is shown as: Untrusted Bitdefender CA. The valid dates are 8/21/2015 to 8/21/2018 and my computer has the correct date and time. On the Certification Path tab, it states: This certificate is OK. I ran a repair on Bitdefender and that did not fix the problem. I completely uninstalled and then reinstalled Bitdefender, and I still have the same problem. Given that I have completely uninstalled and reinstalled Bitdefender on this computer, and I have 8 other PC's also running Bitdefender that don't have this problem, I am thinking that this is a Windows problem. I have searched and not been able to find any references to this type of problem. I'm hoping someone here may have some knowledge or experience with this type of problem.. I really don't want to have to do a complete Windows reinstall.