In the modern age of computing, data is constantly being transferred across the Internet every day. As data travels from computer to computer, there is often little verification about the source of data that a computer may receive. The owner of a website or its administrators are often unknown and unseen. Therefore, it is wise to use anti-virus software to protect your computer from any unintended downloads or installations. It is also wise to know about the possible effects of computer viruses to better identify a computer's behavior.
One of the classic primary signs that a computer has a virus is that it suddenly becomes much less responsive than normal. This usually continues after rebooting the computer as the malicious software begins running again and using system resources. Applications that monitor system resources (such as the Windows Task Manager) of the computer may show a high percentage of the processor or processors already in use, even when a computer user is not running any applications. The majority of the system memory may also be in use and such a situation can also cause the computer to respond slowly. Using the Task Manager in Windows can show a computer user the running processes and can also be used to easily see what applications are using the most memory and processor resources.
Changing of Files
Another main effect of computer viruses is the modification of files on a hard drive or other writable media. Seeing new and unknown files, folders or applications appear on a computer's hard drive is one possible sign of a computer virus. Another possible effect is the modification of files. System files have historically been a common target because modifying a computer's system files can cause an operating system to stop functioning. Modifying software can also disable an operating system's firewall or similar software. Such modifications may be made to enable easier remote access to a computer. If a firewall or anti-virus application appears to have issues in functioning, then it could be a sign of a computer virus.
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Another possible effect of computer viruses is random and surprising behavior. A computer's mouse pointer may start to jump around the screen or stop responding. A computer user should note that this can also happen for other reasons (especially with a wireless mouse). Surprising graphics or applications may also appear on a computer screen, possibly in multiple windows. Some computer viruses have historically been written as pranks and only display an image on computer screens for a programmer to gain personal notoriety. This is obviously not a wise way to prove a person's programming skills, but computer viruses are supposedly often written for such reasons.