The Importance of Time


If you are getting errors about certificate revokation, SmartScreen, Windows Defender definitions, or logging into your live account, there’s a good chance either your BIOS clock, your Windows system time, or both are incorrect. Changing your BIOS clock will probably require you to also change your Windows system time. I found that getting both of these in sync, and correct solved my problems. Read on for a bit more detail.


I recently replaced the motherboard in my PC, because the previous one had died. It was a warranty replacement so I didn’t have to worry about drivers etc, but I did have to do a Windows Activation over the phone because the MAC address and a few other details had changed.  What I didn’t pay close attention to was the time in the BIOS (well, UEFI is more accurate, but whatever), and later the time in Windows itself.

I noticed a few wierd issues with my PC:

  • Every time I ran a downloaded exe, I got an error saying “Windows SmartScreen can’t be reached right now”
  • Windows defender was refusing to download updates. In fact, at any given time it would say that I had installed tomorrow’s update, today.
  • Visual Studio was refusing to renew my Windows 8 App Developer License
  • I couldn’t log into Skype with my Windows Live account
  • I was getting an SSL warning in Chrome saying “unable to check whether the certificate has been revoked”
  • I was getting a similar error through IE (or applications that use it under the hood for talking to the internet) saying “Revocation information for the security certificate for this site is unavailable”

A bunch of googling lead me to look in my BIOS and see what time the hardware clock was reporting. It was wrong, I forget exactly how wrong it was but it was at least 12 hours if my memory serves correctly. After booting back up, I found that Windows Defender was now happily installing updates, and I *think* SmartScreen may have started to behave, but the other issues still presented themselves.

I left it there because I had work I needed to do so I want to the office and used my Windows machine there. Last night I did a bit more googling, which led me to double check my System time in Windows (which had been correct initially). Turns out that after changing the clock in the BIOS, the system time had gone all wack. The time was ok but the date had taken me all the way out to the 26th of December. “How rude!” I thought, “Trying to cheat me out of Christmas!”. Anyhow, I set the clock to the correct date and time, and now it is all good.

Why does this happen? My supposition is that a bunch of the cryptography involved is salted with the current time (I’m pretty sure that this is the case for using Windows Live accounts as they are no doubt based on the same Kerberos implementation used in Active Directory, and Kerberos is very time sensitive).

So, hopefully you’ve come to this page via google because you’re struggling to solve one or more of the issues above. If that is the case, I hope this post helps solve your problems.

2 thoughts on “The Importance of Time

  1. Good evening. I looked into one of your older posts involving your Arduino programming to pull in multiple NMEA sentences from different sources. Yours is one of the very few articles I have seen addressing the issue of using multiple data sources to read with an Arduino. We are using a Mega 2560 R3 but are currently using two separate components for data collection: a NMEA combiner and a serial data recorder.

    We also now have an Adafruit data logging shield to replace the costly serial data recorder. Is there any way you can assist me or you can direct me to somebody who could? I would appreciate it.

    Alex S

    1. Hi Alex,

      I’m unable to help at the moment, and I don’t really know anybody that I can direct you to. I ended up getting a bit stuck because to capture multiple sources I had to use software serial ports, and they take up a lot of your CPU time. I looked at making a pseudo scheduler so I could get other things done between bits (as NMEA is quite slow, so you get reasonable chunks in between), but I got busy with a new job, and haven’t had time over the last couple of years to get it done. These days, I would look into something like Teensy, which has an Arm Cortex M3 in it, which is vastly superior, but pretty darn cheap.



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