Does bitcoin or Blockchain protect against malware attacks that install a trojan to steal data from a device, on which bitcoin application is installed? Cause a trojan can steal the user’s private key, thus his bitcoins can be stolen.
I try to make it short (as this question spreads a wide range…): bitcoin or blockchain do not protect against malware. At the end, bitcoin can be considered as the software that runs a wallet on your computer/mobile. And blockchain is a public accessible data structure. We can forget about blockchain, cause this data structure doesn’t help at all to protect against malware.
So for the wallet: this is a set of data on your harddrive, that contains (somehow) the priv key. As long as your operating system permits access to the storage area of your harddrive, it depends on the protection layer of the OS, how to secure this. Windows has a very long and very strong record of insecurities at all layers (any vulnerability you can think of), and the amount of “protection software” shows clearly, that this is not the optimal operating system for storing value(s). I am not strong enough an expert for mobile devices… When it comes to Unix type OS, the world looks far better, and there are less attack vectors, due to the segregation of duties in the system. Still there are possibilities to “steal” your data, e.g. when you install a (probably unverified) software as admin on your system.
Generally this OS protection topic should be further discussed in the information security area, not here. As long as you store only little value (like you would have Euros or Dollars or Pounds in your real wallet), any unix type OS would do, also mobile wallets. When you go above values of let’s say 1000 Euros/Dollars/Pounds, start thinking about protecting your values (keywords: hardware wallet, cold storage). You find enough references here or in reddit.