How can I protect myself from getting a virus?

In today's world having anti-virus software is not optional. A good anti-virus program will perform real-time and on-demand virus checks on your system, and warn you if it detects a virus. The program should also provide a way for you to update its virus definitions, or signatures, so that your virus protection will be current (new viruses are discovered all the time). It is important that you keep your virus definitions as current as possible.

Once you have purchased an anti-virus program, use it to scan new programs before you execute or install them, and new diskettes (even if you think they are blank) before you use them.

You can also take the following precautions to protect your computer from getting a virus:

Always be very careful about opening attachments you receive in an email -- particularly if the mail comes from someone you do not know. Avoid accepting programs (EXE or COM files) from USENET news group postings. Be careful about running programs that come from unfamiliar sources or have come to you unrequested. Be careful about using Microsoft Word or Excel files that originate from an unknown or insecure source.
Avoid booting off a diskette by never leaving a floppy disk in your system when you turn it off.
Write protect all your system and software diskettes when you obtain them. This will stop a computer virus spreading to them if your system becomes infected.
Change your system's CMOS Setup configuration to prevent it from booting from the diskette drive. If you do this a boot sector virus will be unable to infect your computer during an accidental or deliberate reboot while an infected floppy is in the drive. If you ever need to boot off your Rescue Disk, remember to change the CMOS back to allow you to boot from diskette!
Configure Microsoft Word and Excel to warn you whenever you open a document or spreadsheet that contains a macro (in Microsoft Word check the appropriate box in the Tools | Options | General tab).
Write-protect your system's NORMAL.DOT file. By making this file read-only, you will hopefully notice if a macro virus attempts to write to it.
When you need to distribute a Microsoft Word file to someone, send the RTF (Rich Text Format) file instead. RTF files do not suport macros, and by doing so you can ensure that you won't be inadvertently sending an infected file.
Rename your C:\AUTOEXEC.BAT file to C:\AUTO.BAT. Then, edit your C:\AUTOEXEC.BAT file to the following single line:

auto

By doing this you can easily notice any viruses or trojans that try to add to, or replace, your AUTOEXEC.BAT file. Additionally, if a virus attempts to add code to the bottom of the file, it will not be executed.
Finally, always make regular backups of your computer files. That way, if your computer becomes infected, you can be confident of having a clean backup to help you recover from the attack.