Thanx!
I do not understand then, why whole crypto industry is in fear of an arrival of quantum computers?
Whole crypto industry? No.
Individuals that don't understand cryptography or don't understand quantum computing will often mistakenly believe that "quantum" is a magical word that means "able to instantly break ALL forms of cryptographic functions with as little as 1 qubit". These people tend to be very vocal and like to hear themselves talk, so you see a lot of nonsense from them.
Because what you write there is not known even public key to be cracked?
As has been pointed out by others, not all bitcoin addresses or transactions are the same. There are P2PK transactions where the public key is in the transaction (and there is no address). There are addresses that are hashes of complex scripts that may not use ANY public key at all.
Additionally, in most cases, the public keys associated with the address are broadcast when the bitcoins are spent. This is why it is a best-practice to never use an address more than once to receive bitcoins. Instead, generate a new address for every transaction.
I read some articles and it is written that private key simply leaked from third-party-companies? Am I right?
In many cases bitcoins have been lost due to users trusting some third party to secure their private keys for them.
So not using third parties one should be safe with cryptocurrency?
Unless you fail to secure your private keys yourself. Malware can capture private keys stored on your own computer. Thieves can gain access to any physical storage or trick people into revealing passwords. If you do not have exclusive access to all the private keys associated with a bitcoin address, then you do not have the bitcoins associated with that address.