Assuming a 164 bit number. It's roughly equivalent to finding one atom out of all the atoms that make up the earth. (numbers are for scale, not complete accuracy) It would take one person a thousand years to calculate the same number of hashes as there are atoms in a grain of sand. It would take a million people 1 day to calculate the same number of hashes as 1 grain of sand equivalent. It those million upgraded their systems constantly it would take decades to calculate hashes equal to the number of atoms in a handful of sand. If you expand this out to everyone on the planet after decades you would still only be equivalent to a the atoms of a dump truck full of sand. Also stronger the hash algorithm those times would go way way up. Assuming a 256 bit number and you go into the number of atoms in all the universe realm. Of course this is all moot if someone has physical access to your computer. They can just copy the files out of your directory.