Computer Viruses & Trojan Horses

Viruses and Trojan horses are malicious codes spread over the Internet.

Microsoft defines a computer virus as "a small software program designed to spread from one computer to another and to interfere with computer operation." Viruses are a major threat to computers in homes, businesses and government offices because of their intrusive and destructive abilities. Another type of malware, known as a Trojan horse, is a subversive program that imitates a useful application. The main difference between a Trojan horse (or Trojan virus) and a virus is that the former does not spread itself.

Virus Activity and Symptoms

Once a virus infects a computer, it affects normal operations and begins to show symptoms. Based on the type of virus, and how soon after infecting it is removed from a computer, a virus may corrupt and delete a computer's data automatically, may use email applications to spread itself by mailing copies to all receivers in the address book, or it may erase information from the disk. Common symptoms include slow computer processes, frequent crashes and freezes, inaccessible disks and applications, unfamiliar error messages, distorted menus and dialog boxes and disabled anti-virus controls.

Virus Sources

Computer viruses are most often spread as attachments included in emails and IM (instant messaging) sessions. That is why network administrators advise computer operators not to open emails from unfamiliar sources, and to always check and make sure with the sender about any attachments; typically, the attachment disguises the virus as an image, e-card or an audio or video clip. Another source of viruses is illicit software that is spread through the Internet. When a user downloads software from a questionable site, the virus is secretly embedded with the software. Upon download, the virus detaches from the software and infects the computer.

Trojan Horse Activity

Trojan horses, like some viruses, are downloaded as "harmless" programs. Usually, the malware disguises itself as a small useful application, freely available for download from dubious websites. A Trojan horse is designed to give control of the infected computer to its developer. A Trojan horse is usually split into two parts, known as the server and the client, and works when the client infects a computer and the developer uses the server to control the infected computer. Trojan horses may be used by unscrupulous programmers to hack computers and steal personal information or sensitive information in business.

Malware Removal

Removing viruses and Trojan horses start with obtaining the latest updates of the OS (operating system) and the anti-virus program. OS updates resolve security vulnerabilities, and anti-virus updates enable the program to detect the latest and most advanced malware on the Internet. Regular updates give a computer the best chances of fending off malicious codes. Once the OS and anti-virus are updated, a thorough, full system scan of the computer will be able to identify and locate suspicious software hidden within the system. The anti-virus program can be used to clean (disinfect, quarantine or delete) the malware.

Firewall

Some anti-virus programs have an integrated security feature known as a "firewall" that protects the computer in real time. Enabling the firewall reduces the chances of future instances of infections, because it is able to identify potential attack attempts and take precautionary measures in time. The user can monitor all inbound and outbound Internet traffic, and is alerted in case of suspicious activities.

References

• Microsoft Support: Virus descriptions
• Top Bits: Trojan Virus