How to Attack Blockchain Cheaply?

When people talk about a blockchain attack, the 51% attack is most often mentioned. It is usually said that the attacker must gain dominance over the resource that is used in the given network consensus. 

That should be costly. However, the attacker does not always have to buy the resource directly. What if the resource can be obtained through social engineering, for example, or by hacking several computers? 

It Is Too Expensive Blockchain networks are inherently vulnerable. Their security is based on the assumption that the attack is extremely costly, i.e. that the attacker will not be willing to spend more resources on the attack than honest participants. 

Gaining dominance in holding an expensive resource, i.e. ADA coins in the case of Cardano or hash rate in the case of Bitcoin, Read article: How to Attack Blockchain Cheaply?