[swatkat]

It's more likely a problem with Avast security software, not the website itself. Are you using Avast Anti-Virus or Web/Mail Shield? Avast installs a root certificate to intercept and scan HTTPS traffic[0].

[0] https://itnerd.wordpress.com/2015/05/21/avast-responds-to-my...

[OneTwoFree]

Thanks. I use Avast Anti-Virus. I didn't know they are doing man-in-the-middle. But as I learned, this is quite common for modern antivirus softwares, so I turned off this option in Avast.

[psykovsky]

Why do antivirus seem to be more malicious than the virus they fight?

[iLoch]

Well that sounds like spyware if I've ever heard it.