Proof of Work is an algorithm that is used by different cryptocurrencies – such as Bitcoin, Ethereum, Litecoin – to reach a decentralized agreement between different nodes in the process of adding a blockchain-specific block.

Proof of Stake is an alternative method, a way through which nodes reach a consensus

In short, while Proof of Work is an effective mechanism to secure the blockchain and provides a trustless consensus paradigm, it’s extremely energy intensive because of all the computing power required to solve hash problems. Delegated Proof of Stake (DPOS) aims to solve this. Initially conceived by Dan Larimer, instead of using hardware to solve hashes, he proposed that people in the network vote for “witnesses”. These witnesses are responsible for keeping the network secure

It's probably good for now, because Bitcoin-stealing malware isn't very sophisticated yet: it's mostly clipboard adress-replacing trojans, fake wallets and malware that steals wallet files and tries to decrypt them later or hopes for unencrypted files. However, there's always the risk of more serious malware that tries to steal your keys from memory when they are briefly decrypted, keyloggers that steal your wallet file and wallet password and so on. Virtualization might be not good enough, if I'm not mistaken vulnerabilities like Spectre and Meltdown can bypass them.
This will allow you to sign transactions offline in an even more isolated environment than virtual machine.

It's probably good for now, because Bitcoin-stealing malware isn't very sophisticated yet: it's mostly clipboard adress-replacing trojans, fake wallets and malware that steals wallet files and tries to decrypt them later or hopes for unencrypted files. However, there's always the risk of more serious malware that tries to steal your keys from memory when they are briefly decrypted, keyloggers that steal your wallet file and wallet password and so on. Virtualization might be not good enough, if I'm not mistaken vulnerabilities like Spectre and Meltdown can bypass them.

If you can't afford hardware wallet or dedicated device for cold storage, you can at least get a flash drive, install some secure OS on it (I'm using Tails) and boot your PC/laptop from it, and preferably disconnect other drives beforehand. This will allow you to sign transactions offline in an even more isolated environment than virtual machine.

Blockchain and cryptocurrency are two different things but they are inseparable. Cyrptocurrency is digital currency which can be used in financial transactions and those transactions are automatically recorded in digital ledger called blockchain. Every transaction should be recorded properly for monitoring and transparency of records. The good thing in blockchain is, it is made publicly and cannot be corrupt by hackers. Blockchain protocol tokens serve two purposes today: they protect scarce network resources without introducing centralized gatekeepers, and they incentivize desirable behavior in network participants.

Blockchain and cryptocurrency are two different things but they are inseparable.  Cyrptocurrency is digital currency which can be used in financial transactions and those transactions are automatically recorded in digital ledger called blockchain.  This is same with the existing accounting principle. Every transaction should be recorded properly for monitoring and transparency of records.  The good thing in blockchain is, it is made publicly and cannot be corrupt by hackers.  In this manner, you can see that in every cryptocurrency there is always the blockchain.