Install as FIRST program a decent firewall on your computer, if possible from a usb key you put the installer on it coming from the download from a safe computer.
ZoneAlarm, PC-Tools, Comodo (even if they were producing spywares before...) are good choices.
ALWAYS DEACTIVATE AUTORUN!!! (especially for usb devices)
Activate the display of extensions of your files, some can be fake .zip or .jpg and in fact to be a .exe...
To avoid to catch viruses, don't go on crack/pr0n sites...
Run your Windows as simple user instead of administrator (UAC activated) or if your aren't scared to change your habits use a Linux distro.
Use Firefox with AdBlock and NoScript, as you can catch some shits via adverts/iframes.
NEVER INSTALL ANY TOOLBAR IN YOUR BROWSER (Ask, Winamp, toolbars for emails).
If possible, run it in a Sandbox (
Sandboxie) which is a kind of condom for your computer.
For the hi-risk level stuff (if you can help yourself to use a keygen/crack/warez program), install a second system in a
Virtualbox, do a snapshot before to inject your keygen, and rollback it after.
If you download a program + a keygen/patch, download the original installer from the editor's website (or from a site like
Softpedia).
Then install the clean program on your machine, and do some tests at least in your Virtualbox (which should have an antivirus/firewall too)
Never open joined documents from an email or from MSN.
If you really want to open it, do it in a Sandbox or a Virtualbox.
Always ask for confirmation from your contact if he actually sent you the file.
And even, don't trust it is safe... It can still be infected (macro-virus in office docs...)
Avoid sites like
Facebook which contain a huge quantity of malwares (I know for some of you it will be hard)
By the way, whatever antivirus you could choose it could be defeated since it exists the
KHOBE attack which concern every version of Windows.
NO ANTIVIRUS IS TOTALLY SECURE ANYMORE.
Imagine this scenario:
Your computer is a disco and your antivirus is the gorilla outside checking if you are allowed to enter...
If a guy with tennis shoes (a malware of the bad suburbs

) is trying to enter, he is rejected...
But now imagine a friend of him dressed with a tuxedo, good looking, the gorilla will open the door...
And at this moment, as the door is open, the bad guy runs like a rabbit to jump inside!
This is the system of the KHOBE attack, two processes cooperating, one looks clean to fool the antivirus, the second one uses the open doors.
Always remember, most of the time, the responsible of a viral infection is the user!
Like we say in France, the most dangerous threat is the interface chair-machine.
I'm Technician in Computers and everytime we had a problem, it was because of the stupidity/ignorance of a user
