If you click on a PayPal button and receive the Security Alert that says  "...The security certificate has expired or is not yet valid..." it means that your browser software does not have the latest information needed to read the security certificate.  PayPal's security certificate is valid through 2017.    Receiving this message does not affect the security -- you can still use the PayPal buttons with confidence to securely donate, buy merchandise or pay for membership.

PayPal Technical Support recommends you take the following steps if you receive this security alert:

If you are using Microsoft Internet Explorer and are receiving a Security Alert stating that 'The certificate has expired or is not yet valid' when attempting to access https://www.paypal.com/, it is likely that your browser does not have the newest root certificates installed and is using an older version.
This issue can be resolved by following the steps below:

   1.  Please ensure that you are accessing PayPal directly at https://www.paypal.com/ (rather than a Bookmark or Favorite)  This step does not apply to the PayPal buttons on our website..
   2.  Ensure that your computer's date and time are correct by clicking:
Start > Settings > Control Panel, and double-click 'Date/Time'

If you are still receiving this warning you will need to update the browser's Trusted Root Certification Authorities certificate store by following the steps below:
   1.  Go to http://windowsupdate.microsoft.com and click the 'Scan for updates' link
   2.  Click the YES button when asked to download Microsoft's update package. Microsoft will create a customized update package for your browser, which should include a CA Root update. Typically this is found
under the heading Recommended Updates. If there are any issues or questions with this page or these updates, please contact Microsoft Support.
If this does not resolve your issue you may need to install the newest root certificates from Verisign directly at
https://www.verisign.com/support/site/update.html. Simply click 'Accept'  and follow the instructions to install.
Lastly, if you are still receiving this warning, you should consider upgrading to a newer version of your browser.
We appreciate your patience and understanding regarding this matter, and wish you continued success on PayPal.
PayPal Tech Support
PayPal, an eBay Company