Even technically sophisticated users lose perspective on security at times. We all want breaches of security to be someone elses fault and we dont want to have to deal with the inconveniences of running a secure system.
But there are certain security rules that apply to all computing platforms. These rules are expressed well in an article on Microsofts TechNet site called Microsofts Ten Immutable Laws of Security. These laws are worth keeping in the back, and often the front, of your mind.
Law No. 1: If a bad guy can persuade you to run his program on your computer, its not your computer anymore. The first law, appropriately, is the most important one. Its a truism so true that it often gets dismissed as trite when its actually at the heart of many attacks. It is at the heart of many social engineering attacks, including spyware and almost all e-mail worms, including Bagle and Netsky.
We try to mitigate this threat with such products as anti-virus software, but these can never be perfect. The primary defense must be the one typing at the keyboard, and if you are cavalier about running programs that you get from strangers you will likely end up compromising your computer.
Its only fair to say though that this is also an area in which Microsoft, for complicated reasons, shares some responsibility. The ability for a bad guy to persuade you to run a malicious program is related to your own rights on the computer; if you are running as a less-privileged user, then the program you run is limited in the damage it can do. Microsoft has good tools for limiting the rights of users in a managed corporate environment, but it hasnt made enough of an effort to do so for consumers.
Law No. 2: If a bad guy can alter the operating system on your computer, its not your computer anymore. I really hope this is obvious. Some programs on the computer must be trusted, and—significantly—I lump device drivers in this as well. Microsoft has actually put good protections into Windows against such threats with system file protection, which looks for modifications to critical system files and undoes them.
Law No. 3: If a bad guy has unrestricted physical access to your computer, its not your computer anymore. There is no security without physical security. Consider that someone alone with your computer can boot it up off the floppy or CD drive and run his or her own software while none of the software on your computer can protect it. The attacker could install spyware, compromise your own security provisions, or just wipe out the disk.
Law No. 4: If you allow a bad guy to upload programs to your Web site, its not your Web site any more. "Upload" is such an official way to put this; the real-world way this often happens is to invoke a buffer overflow on the server in order to run arbitrary code on it, but there are other ways it can happen.