Most viruses fall into one of three categories, based on how they spread:
boot sector viruses
Boot sector viruses attach themselves to floppy disks, then copy themselves onto the boot sector
of your hard drive when you turn on or reboot your system. (The boot sector is the set of instructions your computer reads when it starts up.) You can get a boot sector virus only from an infected disk--you cannot get one from sharing
files or executing programs. Since most of today's computers do not require a boot disk to start, these viruses are becoming less common, but they can travel on disks that contain other types of files.
program viruses
Also known as traditional file viruses, these demons attach themselves to executable files associated with other programs. While most of them hook onto EXE or COM files, they can infect any file that your computer runs when it launches a program (including SYS, DLL, BIN, and others). When you start a program containing a virus, the virus usually loads into your computer's memory. From then on, the virus can infect any other program that is executed. Macro viruses are technically a variation of program viruses.
macro viruses
These viruses affect the template (in PCs, usually the normal.dot file) used to create documents or spreadsheets. Once a template is infected, every single document or spreadsheet opened with the program is also corrupted. Because they infect common office applications and can spread between platforms, macro viruses have recently become widespread.
Here's the main thing to note: viruses work only if you execute them, either by running the program they've glommed onto or by booting your system from an infected disk. This point may seem obvious, but most virus hoaxes scare people who don't understand this basic concept.
click below for more virus info...jeff....