Recently I've been getting that little yellow ribbon on Internet Explorer warning me that there's something wrong with the certificate, and also accessing a certain https website shows me the "Certificate Error" page.
I've been able to trace the problem to a missing "Trusted Root Certificate". Now the issue is, I never removed it (and as far as I can remember, did nothing to even "install" it in the first place). Also confirmed that, in another machine, the certificate is there and everything works fine.
How did the certificate disappear from my machine? Since I never installed it, I take it it's some kind of default Windows thing. If so, how do I get it back?