Symmetric algorithms used for encryption, like AES, are still thought to be safe (with sufficient key length – e.g. AES-256 or larger); however, current asymmetric algorithms like RSA and ECDSA (Elliptic Curve Digital Signature Algorithm) will be rendered essentially useless once quantum computers reach a certain scale.
Therefore, much encrypted information that is around today, or over the coming years, will probably be susceptible to decryption one day in the future once quantum computers are generally available (if they will be available at all). The challenge is particularly severe for governments, who have large amounts of secret data with a long "intelligence life" – i.e. it needs to be kept secret for 25 years or more for national security reasons. Protection of this legacy data is not a simple problem, because of both the complexity (this data has been encrypted over the years with a menagerie of cryptographic tools) and the sheer volume of data to be protected.
Mathematicians within academia and government are working on a number of candidate "quantum-resistant" algorithms that cannot be broken using quantum computers; these algorithms comprise what is known as post-quantum cryptography.