How secure are files on an unencrypted hard disc? How secure are files, that I saved on an internal Macbook hard disc using OSX 10.11? I cannot check whether the hard drive is encrypted using FileVault as the machine crashed. I am thinking whether I need to invest 40$ to get it savely formatted by some professionals or just sell it.

If you are not the account owner and don't know the account password, will you be able to read files from my account if you put the hard drive in a new machine?
If the hard drive is not encrypted, then it's not at all secure!

Basically anybody can take the hard disk, put it into an external enclosure and connect it to another Mac to read all files on the disk.