A really good read for linux users. http://www.osnews.com/story/23463/Linux_Security_-_a_Few_Useful_Tactical_Tips Update: For People using Distributions other then Fedora/Ubuntu/Suse. You may not have Firewall software by default. Ubuntu's firewall called ufw is in most repos, like Arch and Gentoo. Ther eis also a GUI. It may be called gufw or ufw-frontend. Ubuntu comes with the firewall without a GUI and turned off, this is because by default Ubuntu has no Open ports. I highly recommend setting up ufw to deny all incoming connections and allow all outgoing. Also if you are hosting any kind of server (be it webserver, ftp, ssh, minecraft) you may need to add an exception for the port. Same goes if you have any port forwarding. Side note: UFW is really a front-end for IPTABLES, which is way more complicated. Hence the name, UFW: Uncomplicated FireWall Side note 2: You can run ufw without a gui from a terminal with the command ufw.