You can also check using Magento's API using the following request from the terminal:
$ curl https://magento.com/security-patch-check/{domain}/{admin path}
Optionally, you can force the API to check in https mode:
$ curl https://magento.com/security-patch-check/{domain}/{admin path}/https
You will get something like this
{"status":"ok","message":"SAFE: This site appears to be safe."}
OR
{"status":"warning","message":"WARNING: This site appears to be vulnerable. Please patch it immediately!"}