One useful safe option for storing archives is an encrypted Disk Image. You can do this using Disk Utility (in the Applications/Utilities folder). Collect your old backups in Zip files, then use Disk Utility to create a New Disk Image and select "Encrypted" in the type drop-down. Give it a good, strong password (of course) and copy the zip file(s) into the encrypted Disk Image. When you unmount the image, its contents will be encrypted. Every time you want to read the contents of that image, you have to mount it (by double-clicking on it), and you need to provide the password to do that.