Viruses are not the only threats to your computer. Due to the widespread use of computers and the Internet, other threats have emerged that can be extremely destructive, resulting in loss of data and productivity. The following are the most common types of computer threats.
A virus is a piece of computer code written with the sole intention of replicating itself. A virus attempts to spread from computer to computer by attaching itself to a host program or file, typically without user knowledge or permission. Once a virus infects your computer, it can damage your software, your hardware, and your files. Viruses range from the mildly annoying to the highly destructive. They can be classified using multiple criteria such as origin, techniques, types of files they infect, where they hide, the kind of damage they cause, and the type of operating system or platform they attack.
A worm, like a virus, is designed to copy itself from one computer to another, but it does so without having to attach itself to a host program or file. A worm generally spreads without user action and distributes complete copies of itself across networks. A great danger of worms is their ability to replicate in great volume. When new worms are unleashed, they spread very quickly, clogging networks and causing them to slow down and even collapse.
Unlike viruses, Trojans do not reproduce by infecting other programs or files, nor do they self-replicate like worms. Trojans are computer programs that appear to be harmless, but in fact contain malicious code. When a Trojan is executed, it can delete your files and compromise the security of your computer. Trojans spread when people are lured into opening an e-mail attachment or downloading and running a file from the Internet because they think it comes from a legitimate source.
It is important to know the difference between a real virus threat and a virus hoax. Hoaxes are not viruses; they are false messages sent by e-mail warning users of a non-existent virus. Virus hoaxes often include technical terms or agency names to mislead users into believing that they have received a warning about a real virus. The intention is to cause panic and trick users into taking immediate action to protect themselves from the virus, often leading to negative results. Users are advised not to pay attention to these misleading warnings and to delete these messages without e-mailing them to others.
Ransomware is a type of malware that prevents or limits users from accessing their system, either by locking the system's screen or by locking the users' files unless a ransom is paid. More modern ransomware families, collectively categorized as crypto-ransomware, encrypt certain file types on infected systems and forces users to pay the ransom through certain online payment methods to get a decrypt key. For more information see http://www.trendmicro.com/vinfo/us/security/definition/ransomware.