Understanding Cryptocurrency Security: Bitcoin Botnet-Miners, Malware, and Attack Vectors

What are Bitcoin botnet-miners and how do they operate?

Security
?How do bitcoin botnet-miners, like Miner Botnet, operate and what measures can be taken against them?
?What malware, e.g., Cryptolocker, have been used by cybercriminals to obtain cryptocurrencies, which vulnerabilities did they exploit and what mitigation can be adopted against them?
?What attack vectors have been used to exploit cryptocurrencies (e.g. Skype and Yahoo, and how to counter them?
?What attacks on cryptocurrencies have been theoretically identified (e.g., Double Spending Attack  and Block Discarding Attack and how could they be avoided/mitigated?
?What has evolved, and what are the differences and similarities between existing (and/or extinct) cryptocurrencies such as Bitcoin, Litecoin, Ripple and Peercoin?
What incidents affecting cryptocurrencies (e.g. security breaches on Mt. Gox – the largest Bitcoin exchange, and on Bitcoinica online trading site for Bitcoins) show us about risks and possible mitigation