Backup
regularly. Make sure there's a copy
of whatever is important to you somewhere
other than your computer. An external hard
drive or on-line service or at least a couple
of flash drives.
Install a recognized anti-virus:
read a couple reviews or ask some friends what
they use. The most popular programs around
here (in no particular order) Norton,
Kaspersky, NOD32, McAfee, AVG, Avast. For home
use, AVG and Avast have free versions.
If using Windows XP, install Microsoft's Windows
Defender unless your anti virus won't
work with it.
Backup
Regularly. I can't say it enough.
Consider a program such as Acronis True Image
or Norton Ghost for simple restore of the
complete operating system.
NEVER install any program that pops out of
nowhere and tells you your computer is in
grave danger. Have you seen something like
this?
A common ploy to get unsuspecting people
to buy software they don't need is to
place a pop-up ad on a website that makes
it seem that your computer has already
been compromised. The threats mentioned
are bogus, possibly mentioning files that
do not exist, or as here, network attacks
that never happened. If you accept the
download, you'll see warnings like those
above popping up incessantly.
If you click on the "Yes" button, you'll
be asked to buy some software that does
nothing or is actually something evil.
You'll need some expertise to get rid of
it.
If you've already got one of these rogue
anti-virus programs, try MalwareBytes
Anti-Malware. The free version is very
good. The pay version will provide protection
while you work rather than just on-demand.
Backup
Regularly. Are you backing up
everything? Don't forget e-mail and contacts.