Security

The most likely computer “disaster” is due to human error: probably brought on by system reconfiguration, or accidental damage to files by the user. The new user generally believes this to be caused by a virus.

After human error, in diminishing order of likelihood, the problems are:
    hardware failure;
    software malfunction;
    theft;
    virus/malware;
    and other miscellaneous - fire, water ingress etc.

The solution:  user data needs to be backed up.  This is a chore and people won't do it unless the penalty for not doing it is apparent to them - generally after the event.  I can think of no-one who regretted backing up their data, and plenty who regret not doing.  The best method is to automate it so that users have only minimal involvement in the process.
Viruses, Worms, and Trojans are sometimes collectively termed Malware. Broadly speaking, viruses are deliberately corrupted bits of programs that infect other programs and perform malicious tasks.  Worms are free-running programs that exploit networks to copy themselves onto other machines. Trojans are malicious programs installed by the user in the mistaken belief that they served another legitimate purpose. The above is necessarily a