Cryptocurrencies CANNOT be trusted. Here's why...

What happens when you exchange digital currency?:

-The transactions are compiled into a block of data.
-The block is encrypted into a hash value.
The encryption process is paramount. It is an algorithm that is easy to calculate but extremely hard to do in reverse (like factorization). The resulting hash value is a unique property of the block of transactions and any tampering with the records would be obvious because it would change the hash!
-New transactions are next gathered together into a new block and added to the existing hash value. This is then encrypted to create a new hash for the new block. This is added to the next list of transactions when they are encrypted, and so on. The result is a chain of blocks that each contain the hash values of all preceding blocks, hence the term blockchain!
-All the computers that store the blocks regularly compare their hash values to ensure that they are all in agreement. Any computer that does not agree, discards the problematic records.

Now that you know how it works it is easy (though of course easier said than done) to see how one could game the system:
The trick would be to change the list of transactions in his favor, but in a way that leaves the hash unchanged.
This can be done by brute force. Specifically:
-you change a record, encrypt the result and check whether the hash value is the same.
-If not, you try again and again and again until you end up with a hash that matches.

Whaa?
How come no one does that then?

That's because there so many combinations that the chances of finding the same hash for two different transactions are practically zero. Even using the most powerful computer in existence to speed up the process would still take millennia!

Right then, so the title of this steemit post was compete and utter BS?
Hmmm not quite....

Researchers, governments, universities, tech companies, have all entered a race to build a new type of computer that is called Quantum Computer.
Without getting technical at all, and in purely layman's terms, a Q.C. will be -at least for certain types of tasks- thousands, perhaps far more, times faster than conventional computers.
You may think your flashy new Intel core i7 PC is blazing fast. Or perhaps you are even a lucky owner of that insane new core i9 CPU that has 16 cores and 32 threads!
32 threads means it can run 32 processes (e.g. calculations) in parallel. That will surely help with finding the hash, right?
No, no, and again no. It would make very little difference (Instead of millions of years, millions of years minus something! :P ).
A Quantum Computer will be able to do an insane amount of computations in parallel (not just 32). Think something like a few days of computation instead of millions of years!

I follow the developments very closely and I can tell you that we won't have to wait very long for the arrival of the first Quantum Computer. It's just around the corner.
When (and not if) it arrives it will send cripples to the whole financial system. Suddenly no security system will be secure. And every cryptocurrency's value will be just a tampering away.

But I'm never a pessimistic one, neither a technophobe. Researchers are already looking for ways to safeguard that not-so-distant future. Quantum encryption for example is a thing. Quantum telecommunications also.
Though protection will be limited to upgraded infrastructure only. Anyone caught still using conventional systems when the first Quantum Computer arrives will be totally unprotected. This is why it is a race. A race far bigger than the space race between the USA and the Soviet Union of the past. And unlike the space race whoever wins this time may not be so vocal to tell the world about it!