Update your Internet Explorer 8

Microsoft has released the IE8 security patch.  You'll probably see it come in automatically tonight; surprise overnight reboot is what you'll experience probably.  I'd just be safe and do it now with Start->Windows Update and go through the prompts.  It's a fast update and does require a reboot.

Still don't forget to keep the anti virus software up to date.  If you don't have any get it.  AVG is a free option.