How quantum computing will change security
Quantum computers are set to change all of that in a drastic way. As an example, forms of RSA are used in secure websites and email systems (notice the https:// instead of http:// on these pages). RSA is based on how difficult it is for computers to factor integers, and is used in almost all public-key cryptography (cryptography that is used across an open network). Quantum computers are adept at factoring integers and if the problems holding them back were solved they would quickly make RSA obsolete, compromising one of the most popular forms of secure communications over the Internet.
Rather than using security that is based off of the difficulty of factoring integers, other lattice-based cryptography or systems based on problems in coding theory. Quantum computers are not yet known to crack those systems easily, but quantum algorithms have far more potential than classic algorithms for problem solving.
While effective quantum computing may not arrive for some time, when it does land it will completely alter the security landscape.