Bitcoin is vulnerable. Alright, alright, relax, it is complex, beautifully created, insanely fun, but, it is still vulnerable. It has layers and layers of security, but the world has layers and layers of delinquent tendencies in individuals.
Bitcoin was created to combat ideas like inflation, monopoly and government centralization in the economy. This could be dealt with very well now because bitcoin means the elimination of big financial intermediaries. This changed the structure of the money economics. Bitcoin had to be secure enough for people to use. And it became secure. But, then, was it safe enough to defend itself from this very structure of its own?
And that brings us to vectors. Attack vectors are set and distinguishable ways for attackers to attack bitcoin. Most of these are inside jobs. Bitcoin can be attacked by a 51% majority attack, an eclipse attack, a Sybil attack, among others.
These attacks are not the only threats to bitcoin, there are other internal and external threats too. But, that is our headache for another time.
The Eclipse Attack
An eclipse attack involves the adversary targeting a specific node (as opposed to the network as a whole) so as to cut off all of their inbound/outbound communications with other peers (which effectively suffocates the victim).
A successful iteration of this attack results in the victim receiving a warped view of the blockchain. This means that the attacker is casting an eclipse on a part of a node or a complete node and this is making a chunk of the larger blockchain invisible for the time being. During this masking, the opponent can use either to cause general disruption and to segregate the targeted peer from other nodes, or as a springboard to mount further attacks.
By isolating a portion of rival miners from the chain, you remove their hash-power from the competition, thus enabling you to commandeer a greater percentage of the total hash-power with your existing hardware.
The attacker could also double spend during this time and the poor innocent people whose actual money may be at stake find out the hard way.
There is another one of this attack, which is the N-confirmation double-spend, where an eclipsed miner includes the transaction to said merchant into a block, prompting the merchant to release the goods, but this is done before the miner is ‘uneclipsed’, orphaning the block containing what appeared to be a valid transaction.