While the support from good consensus algorithm and good miner hardwares are essential for scaling the network, the concerns for network security is also a major problem. What we could think from Bitcoin is that although it is slower than any altcoins or different Blockchain solutions, it has one of the most secure and redundant Blockchain security in the world.
The advantage of proof-of-work consensus algorithm is that it allows no one to revert or interrupt the content of Blockchain ledger. Now days there are lots of financial crime and most of them are related with counterfeit money or scams related with cash, what we could tell about Bitcoin is that if you know how to use the coin correctly, it is one of the most secure banking system when it combines with the inherent tools like multi signature wallet or cold wallet system.
It is the common knowledge that Bitcoin uses public key system and when the matching private keys are fully controlled offline, you would be able to generate the necessary information to build the transaction online and sign them offline with the matching keys, submit the raw transaction to one of the Blockchain nodes available on the network and wait for the confirmation, once the transaction is confirmed it is considered as secured since they are not able to be reverted by anyone unless the network is being centralized like the non-blockchain systems do.
However, due to the low participants of the network on other Blockchain systems, some Blockchain may suffer from 51% attack which is an exploit for the unsecured Blockchain platforms and they are being dominated by the specific 3rd party unlike Bitcoin. Multiple Blockchain developers have worked to prevent this problem and therefore there are variety of Blockchain consensus algorithms have been designed and developed to secure the alternatives.
Security of any kind of payment network is essential and it has to be done by the developer party of the platform, for example if you are opening a new website for selling goods online however you have not considered about cryptography of payment information, the information of your clients would likely to be abused for fraud and therefore there will be no clients who wants to risk their financial information for buying goods.
Like the above security concerns, no one will want your transaction to be abused or modified by the unwilling 3rd party and thus you will need a secure payment solution to cover against malicious ones, that is why Bitcoin has developed and implemented proof-of-work consensus algorithm to combat against financial crimes and become one of the most secure money that has been ever made.
Bitcoin prevents confirmed transactions being modified or interrupted by duplicating every transaction that has been made since the beginning of the Blockchain which is called a genesis block, and it is being verified by node manually when the node receives new information about the Blockchain or what we call it sync the Blockchain, it calculates the cryptographic hashes about block headers and merkle routes.
Some people think that Blockchain is slow due to slow sync speed but it becomes slower if the Blockchain has a massive amount of transactions that has been deployed since the beginning due to it’s verification process inside the node. Merkle roots of the transaction is being recalculated on every peer nodes and proves if it is the right transaction to make sure it is not being replaced by the fake ones.
Not only the sync process is special also the generation of the transaction is unique, not every nodes are participating for including transactions on the nodes. To prevent any technical fraud on the network, nodes are participating in some kind of computing power and those who have the dominant power in the network is being elected as a trusted node and they include transactions into the chunks of datas which is called a block and the whole process including calculation of the nonce and block headers is needed for proof-of-work consensus Blockchains to pick the most honest nodes in the network.