I have a problem with my Windows XP notebook. Suddenly sites like facebook and my email provider (gmx) throws unknown https certificates after trying to login. This error occures only on this xp machine, on my other computer (Windows 7) the websites do not throw any errors.
I am frightened that something has infected my Windows XP notebook. I could not find any viruses and have checked system32/drivers/etc/host file - There are no entries.
I also tested multiple browsers (IE and Firefox). I deactivated most plugins in the browsers.
Any suggestions are welcome. How can it be possible that https certificates are not trusted / corrupted suddenly?