Law #1: If a bad guy can persuade you to run his program on your computer, it's not solely your computer anymore.
Law #2: If a bad guy can alter the operating system on your computer, it's not your computer anymore.
Law #3: If a bad guy has unrestricted physical access to your computer, it's not your computer anymore.
Law #4: If you allow a bad guy to run active content in your website, it's not your website any more.
Law #5: Weak passwords trump strong security.
Law #6: A computer is only as secure as the administrator is trustworthy.
Law #7: Encrypted data is only as secure as its decryption key.
Law #8: An out-of-date antimalware scanner is only marginally better than no scanner at all.
Law #9: Absolute anonymity isn't practically achievable, online or offline.
Law #10: Technology is not a panacea.