Computer Network Administration

Q2\ The client connected to the internet, the user (client), browse one of the hacking sites, which led to the virus's entry to the computer, and caused the collapse of the Hard Disc and RAM is damage. 1) How does the virus enter to the computer? Note, the computer contains an anti-virus (update) & firewall system is work. 2) What is the solution, in your opinion, as a client in one hand, as an administrator in another hand? 3) As an administrator, what do you do to avoid repeating the previous case (1)