If you're storing sensitive information on your computer, then try using TrueCrypt:
http://www.truecrypt.org/
This lets you store your data very securely, and apart from entering a password when you want to access those files, you don't know that it's being encrypted.
As for securely erasing files:
http://www.gpg4win.org/
As well as letting you securely send things in email to others, it also has a secure file erase feature.
Both are free software, so should be free from any 'backdoors'.