Explain about the viruses in detail

Note 1: Viruses don't just infect computers, they may also affect mobile phones, MP3 players etc. - any device that can download files from a source such as internet is potentially at risk.

Note 2: Backing up may allow files which have become corrupted/lost (because of hacking or viruses) to be reinstated; though, this wouldn't recover the system nor would it prevent viruses/hacking affecting a system in the first place.

Note 3: Other problems like spam, pop ups, cookies, etc. are more of a nuisance (albeit they can considerably slow down operation of a computer system) and can be made inactive or blocked (as they can become active without user's knowledge) using appropriate software.