Yahoo! Marriott International. Myspace. Under Armour. EBay. LinkedIn. Just what do these large companies have in common? The answer, as you may have guessed, is that these six corporations have been the victims of the biggest data breaches in the 21st century, with the number of those affected ranging from 117 million executives (LinkedIn in 2012) to as many as 3 billion users (Yahoo in 2013). Such mega virtual break-ins can cost companies hundreds of millions of dollars, but even standard data breaches can be expensive, especially after taking into account the loss of reputation and customers.

Scary as that may sound, the past may have been merely the prologue. Since the 1970s, the RSA cryptosystem, which uses very large prime numbers to create public keys that serve as the basis of the security protocol for data communicated between Internet applications, has proven to be relatively effective. Although Peter Shor of Bell Labs published a paper in 1994 showing that a quantum algorithm could crack the RSA cryptosystem, machines that can run such an algorithm haven’t been developed—yet. It has therefore been possible to develop bigger public keys faster than computers have speeded up, ensuring that the RSA cryptosystem continues to work.

It’s unlikely to stay that way much longer. Scientists are getting closer to developing a quantum computer, a new kind of system that can execute in minutes calculations that would take hundreds of years to complete on the world’s fastest conventional supercomputers. These machines will enable hackers to decipher public keys, and break through the security of almost any encrypted device or system. When exactly a quantum computing-caused Cyber Doomsday will dawn is unclear, but it could happen in just 10 years’ time.