viruses

i have just been doing a quiz based on different computer viruses and the harms of the viruses,
the different types of viruses are: trojans
worms
logic bombs and time bombs
macro virus
resident virus
image viruses
screensavers
script viruses
stealth viruses
mail bombs
backdoors and rootkits

The harms of the viruses are:

Trojans: Trojans normally claim to do something useful but are actually malicious. One major difference between Trojans and true viruses is that they do not replicate. Trojans contain malicious code that can cause loss or theft of data. Trojans must be invited onto your computer, eg: by opening an email attachment or downloading and running a file.

Logic bombs and Time bombs: Like other viruses, Logic bombs are designed to cause harm to your computer. Logic bombs, however, only trigger when specific conditions are met. For example a computer programmer may insert code into a payroll program that deletes files if her name is not found on the list. This means that files will be deleted if she is ever fired. A company named Omega Engineering lost millions of dollars as a result of a logic bomb left by a former employee.