While formal verification of the correctness of computer systems is possible, it is not yet common. Operating systems formally verified include seL4, and SYSGO's PikeOS – but these make up a very small percentage of the market.
Two factor authentication is a method for mitigating unauthorized access to a system or sensitive information. It requires "something you know"; a password or PIN, and "something you have"; a card, dongle, cellphone, or other piece of hardware. This increases security as an unauthorized person needs both of these to gain access.
Social engineering and direct computer access (physical) attacks can only be prevented by non-computer means, which can be difficult to enforce, relative to the sensitivity of the information. Training is often involved to help mitigate this risk, but even in a highly disciplined environments (e.g. military organizations), social engineering attacks can still be difficult to foresee and prevent.
Enoculation, derived from inoculation theory, seeks to prevent social engineering and other fraudulent tricks or traps by instilling a resistance to persuasion attempts through exposure to similar or related attempts.
It is possible to reduce an attacker's chances by keeping systems up to date with security patches and updates, using a security scanner or/and hiring competent people responsible for security.(This statement is ambiguous. Even systems developed by "competent" people get penetrated) The effects of data loss/damage can be reduced by careful backing up and insurance.