What operating system are you on? Are you using a HDD or a SSD? have you ever had sensitive things unencrypted on your drives? If you are on windows you could just do FDE with Truecrypt, it overwrites what is on your drive with an encrypted version of it, possibly/probably not as safe as doing Secure Erase of the entire drive and encrypting it first thing, but it is most likely fine. If you have a SSD and it has ever had sensitive information on it in a non-encrypted format, you are fucked because of wear leveling. SSD need to be encrypted first thing or else they are insecure as soon as they have anything sensitive on them that is not encrypted. Same goes for your USB drive as well, if it is fresh or never has had anything sensitive on it you should just encrypt it with Truecrypt, otherwise you should probably toss it honestly. If you are on Linux it is much easier to encrypt at install time than later on, but you can still configure FDE from in an already installed OS. I have never done it except at install time , but I can probably find a tutorial and walk you through it if it is a requirement of yours.