In cryptography, the RSA and ECC algorithms which we use primarily for asymmetric cryptography are susceptible to Shor’s Algorithm in quantum cryptography. Cracking those algorithms with classical computing is seen as requiring thousands of years, which is why we use them so heavily for things like TLS. Not so with quantum computing.
There’s a concern that threat actors could capture encrypted data today, store it, and if it’s still valuable with quantum cryptography becomes viable, crack the encryption and get the data. This leads to Mosca’s theorem, which is basically a calculation of how long your data is considered valuable for with how long it is going to take you to get to post-quantum cryptography (cryptography that isn’t susceptible to being broken by quantum cryptography) and comparing that to when quantum cryptography becomes viable. If you’re sum is greater than the viability date, you’re data is at risk.
So the big question is what’s the date? There’s been a lot of forecasting. Anywhere from 2031 to 2050. Well, Google just moved up their prediction to 2029. In other words, 3 years from now. Here’s the post where they announce that new date: