The caller wants to know if backing up data to DropBox is secure? He's worried that backup companies have access to his sensitive data. Leo says he can encrypt the data, and he alone has the keys to that. So if he loses it, he's out of luck. DropBox will accept secure encrypted data. If he's looking for a cloud-based encryption backup option, SpiderOak is an option, though it's a bit clunky. VeraCrypt is another.
Mark is having trouble encrypting his hard drive in Windows 8.1. He's told it's encrypted by default, but Leo says if he can't get it turned on, then his hardware probably doesn't support it. Mark should look for TPM 2.0 support. Users also need support for Windows connected standby feature. So if he doesn't have all that, he'll have to get a third party encryption utility. TrueCrypt is free and open source, but unfortunately, they've given the government a back door.