Lecture2

A virus is malicious software, which attaches to another program to execute a specific unwanted function on a computer.
A virus is a malicious code that is attached to legitimate programs or executable files. Most viruses require end-user activation and can lay sleeping for an extended period and then activate at a specific time or date. A simple virus may install itself at the first line of code on an executable file. When activated, the virus might check the disk for other executable, so that it can infect all the files it has not yet infected. Viruses can be harmless, such as those that display a picture on the screen, or they can be destructive, such as those that modify or delete files on the hard drive. Viruses can also be programmed to modify to avoid detection. In the past, viruses were usually spread via floppy disks and computer modems. Today, most viruses are spread by USB memory sticks, CDs, DVDs, network shares, or email. Email viruses are now the most common type of virus.