Indeed bitcoin attracted so much attention and I do believe some would attempt to attack the blockchain to gain control all the funds exist. But it would really be a long shot to do that probably with a super ASIC computer miners will perform a brute force attack but like I have mentioned, its a long shot.
Application-
Specific
Integrated
Circuits [1] can only perform one task (the one they were created for).
Miners ASICS do calculate SHA256 hashes. They can't start bruteforcing private keys.
Recently reported that many computers infected with bitcoin virus.
Bitcoin virus?

Professional bitcoin diggers will set up a system to infiltrate the computer to steal data and dig a bitcoin. They will receive free BTC.
Professional bitcoin
miner don't do that.
Its the blackhat developer who creates malware which will then mine coins for them.
[1]
https://en.wikipedia.org/wiki/Application-specific_integrated_circuit