PayPal has been sending emails about required security upgrades for a while now. If you accept PayPal on your store, you've probably gotten at least one.

There's one item in the email that may cause you some concern:
 
Please rest assured that there's no action required on your part. These messages are based on tests performed prior to changes we've already made to our integration with PayPal.

You can verify this by contacting PayPal and asking them to scan your site again: they'll probably tell you that everything's fine.

In the unlikely event that there is some sort of problem, please contact us right away so we can look into it.