|The way to be sure is to first have a set of restore disks for your unit. Then format the hard drive using FULL format. Then use the restore set to re-install everything. |
This will not insure no one can recover anything but makes it less likely. Be sure to provide the restore disks with the laptop.
There are programs that can wipe the drive more thoroughly.
Just a point to mention. If you keep sensitive data on your computer you are always at risk. The unit might be lost or stolen or you may be hacked. Best to not store things you can't afford to have other gain access to. Bank and credit card access come to mind.
I don't store any passwords on my hard drive. I don't let many passwords be saved. The ones I do are not going to cause me to lose money or my identity.