Ah, we're finally going to talk a bit about straight science and math.
The people who are doing algorithms classify them as two kinds: the easy one—the one that takes a very small amount of resources—and the hard one, which takes a large amount of resources. Of the two, if I want to be a bit more technical, one takes an exponential amount of resources compared to the other.
The algorithms that are resistant to quantum computers are the ones for which we haven't found a quantum algorithm that turns a hard problem into an easy one. The usual one, which is used for logging into your bank, called the RSA algorithm, is hard for a classical computer; that is, if you want to factor a large number with many bits in it, it takes an exponential number of time in the number of bits of the number that you want to factor.
We have a quantum algorithm that takes that algorithm to an easy one on a quantum computer, but there are other mathematical problems that are used to encrypt information that have remained hard on both a classical and a quantum computer.