Bitcoin Forum

We all know that cryptocurrencies are susceptible to 51% attack and that anyone who has that much power will be able to reverse or create new coins out of thin air. I'm curious as to how companies are able to prevent this attack? Since when they first launch their own coins like Dogecoin, people who is already mining ETH and BTC should already have a huge amount of hashing power so if they were the first to jump into dogecoin, wouldn't they immediately own more than 50% of the hashing rate and that would mean they can easily control the network for that short period of time until more users jump in or is my understanding of this wrong?

You can't create coins out of thin air.
They run different algorithms. Altcoins are worth nothing at the start and they are usually not very well known or used so there is really nothing to gain by attacking the coin with a 51% attack to reverse transactions. The attacker would however be wasting their time trying to do so and would rather just mine a profitable or well-known coin or just mine legitimately.

Any person with that much power will be able to retain the longest chain by himself. This means, that if he wants to reverse a block that was previously generated by the “honest” miners, he can. Although, he can't create coins out of thin air, because of consensus.

You'll have to understand, though, that most of the times, it's not worth to do that. You see, the PoW algorithm is written in a way to make it more profitable for someone to extend the chain, rather than to attack it. If the chain is attacked, then the coin's value will drop dramatically, since it's losing its point. Thus, he'll be left with some useless units instead of being able to generate the majority of those coins.

Oh I see, thank you for clearing up my doubts

A POW project can avoid being 51% attacked by being secured by another coin's hashrate i.e. 0xMR on Ethereum or Syscoin with Bitcoin. Another option is Komodo and projects built on Komodo, they have a mechanism that prevents 51% accounts.

The 51% attack is interesting for such coins, from which you can profit from the attacks.
Ethereum (ETH) Nethash 588 Th/s a
Dubaicoin (DBIX) Nethash 0.26 Th/s.
Does it make economic sense to attack this coin?
There are a lot of new coins and it is unprofitable to attack coins that cost very little or have a small Nethash

Nobody is going to waste their time in making 51 attack on a new coin or an unprofitable coins. Bitcoin and ethereum is no longer susceptible in being attacked anymore due to large hash rate. New coins need time to be accepted. So if a unvalued coin is attacked, people will soon abandon it.
 

Big companies always have a strong defense base that is private, but not a few thieves know their weaknesses. no matter how strong the defense system was. because the internet can be compromised at any time.