VIRUSES

Virus is a small computer program that is designed to give someone control over your computer. Viruses usually attach itself to other programs. For example if the program is infected with the virus and you run it. It most likely will reproduce itself to other programs or make your system unstable.
Viruses can be distributed by emails as attachment. Once you click on the email it will infect your computer and send itself out to all your contacts in email address book.
A worm is a special software that scans computer networks for specific security holes. Once if finds them it infects computer and replicates itself.
Trojan horses are computer programs that pretend to be something else. For example you click on mp3 song but instead of listening to the song your computer crashes.
Spyware is similar to malware it a small software designed to collect user data without him / her knowing it.
Malware short for malicious software. Malware is a any type of software that is designed to work against you. Such as viruses, worms, spyware, trojan horse. A lot of times malware will give you pop up window telling you your computer in infected and to go to certain website and make a payment for bogus antivirus software.
If you experience any of the above it is a good idea to update your antivirus software or if you don't have one seek help online. There are a lot of very reputable remote computer places than can repair your computer remotely without any down time.