What Is a Cyber-Attack?

1. What a Cyber-Attack Looks Like

Who carries out cyber-attacks and for what purpose?
Is it military or industrial spies? Or is it hackers?
Spies seek to obtain useful information for their own
countries and companies, such as military secrets and
information on advanced research. On the other hand,
the cyber-attacks we normally encounter are aimed at
something that will benefit the attacker, such as personal
information or money.
Since spies must accomplish their objective, they will
attack with any and all means, and try to intrude no matter
how strong security is. They are a problem and there is no
way to completely stop them for now.
Meanwhile, cyber-attacks for profit are a business
for attackers. For example, given that they will avoid

something with strong security because it takes time and
effort (≈ the cost is too high) and attack things that take…