I am using Avast! 7 Free Edition but one of our PC's (Computer Shop Server) still got infected by a HELLO WORLD! (idk what kind of threat is this, but perhaps it came from a customer's USB) on each Local Disks (C:/ & D:/) and recently any Internet browsers aren't working despite a proper connection. I'm in dilemma of formatting it. And also I'm looking forward to put USB Disk Security or any similar software on it once I reformatted it. Hoping for your expert suggestions. Thanks a lot!