1. What is a computer virus?

A computer virus is a program designed to spread itself by first infecting
executable files or the system areas of hard and floppy disks and then
making copies of itself. Viruses usually operate without the knowledge or
desire of the computer user.

2. What kind of files can spread viruses?

Viruses have the potential to infect any type of executable code, not just
the files that are commonly called 'program files'. For example, some
viruses infect executable code in the boot sector of floppy disks or in
system areas of hard drives. Another type of virus, known as a 'macro'
virus, can infect word processing and spreadsheet documents that use
macros. And it's possible for HTML documents containing JavaScript or other
types of executable code to spread viruses or other malicious code.

Since virus code must be executed to have any effect, files that the
computer treats as pure data are safe. This includes graphics and sound
files such as .gif, .jpg, .mp3, .wav, etc., as well as plain text in .txt
files. For example, just viewing picture files won't infect your computer
with a virus. The virus code has to be in a form, such as an .exe program file or a Word .doc file, that the computer will actually try to execute.

HijackThis™ is a free utility which quickly scans your Windows computer to find settings that may have been changed by spyware, malware or other unwanted programs. HijackThis creates a report, or log file, with the results of the scan.

IMPORTANT: HijackThis does not determine what is good or bad. Do not make any changes to your computer settings unless you are an expert computer user.

3. How do viruses spread?

When you execute program code that's infected by a virus, the virus code
will also run and try to infect other programs, either on the same computer
or on other computers connected to it over a network . And the newly
infected programs will try to infect yet more programs.

When you share a copy of an infected file with other computer users,
running the file may also infect their computers; and files from those
computers may spread the infection to yet more computers.

If your computer is infected with a boot sector virus, the virus tries to
write copies of itself to the system areas of floppy disks and hard disks.
Then the infected floppy disks may infect other computers that boot from
them, and the virus copy on the hard disk will try to infect still more
floppies.

Some viruses, known as 'multipartite' viruses, can spread both by infecting
files and by infecting the boot areas of floppy disks.