Steve is worried he's being spied upon online. He gets a popup on his 4G data connection that says "network may be monitored by a third party." Leo says that's exactly what Superfish has been doing. Certificates get issued by various browser authorities like Google. If he doesn't like it, then he should try another browser.
Often though, the most common cause of expired certificates is a dying battery that keeps track of computer time. It will cause the certificate to appear out of date. With Android KitKat, Google does something called "Certificate pinning," which creates an unnecessary warning message. As long as he's on a secure network, he should be fine. Check out this article - http://geektaco.blogspot.com/2013/11/android-kitkat-network-may-be-monitored.html
Steve is also interested in RaspberryPI computers. Leo says to check out KnowHow on the TWiT Network. They do a lot of stuff on Raspberry Pi.