I found this posted elsewhere and thought that EVERYONE should know them all. Here is one of my favs, read the MS link for more.

Law #3: If a bad guy has unrestricted physical access to your computer, it's not your computer anymore
Oh, the things a bad guy can do if he can lay his hands on your computer! Here's a sampling, going from Stone Age to Space Age:

  • He could mount the ultimate low-tech denial of service attack, and smash your computer with a sledgehammer.
  • He could unplug the computer, haul it out of your building, and hold it for ransom.
  • He could boot the computer from a floppy disk, and reformat your hard drive. But wait, you say, I've configured the BIOS on my computer to prompt for a password when I turn the power on. No problem – if he can open the case and get his hands on the system hardware, he could just replace the BIOS chips. (Actually, there are even easier ways).
  • He could remove the hard drive from your computer, install it into his computer, and read it.
  • He could make a duplicate of your hard drive and take it back his lair. Once there, he'd have all the time in the world to conduct brute-force attacks, such as trying every possible logon password. Programs are available to automate this and, given enough time, it's almost certain that he would succeed. Once that happens, Laws #1 and #2 above apply.
  • He could replace your keyboard with one that contains a radio transmitter. He could then monitor everything you type, including your password.

Always make sure that a computer is physically protected in a way that's consistent with its value—and remember that the value of a computer includes not only the value of the hardware itself, but the value of the data on it, and the value of the access to your network that a bad guy could gain. At a minimum, business-critical computers like domain controllers, database servers, and print/file servers should always be in a locked room that only people charged with administration and maintenance can access. But you may want to consider protecting other computers as well, and potentially using additional protective measures.

If you travel with a laptop, it's absolutely critical that you protect it. The same features that make laptops great to travel with – small size, light weight, and so forth—also make them easy to steal. There are a variety of locks and alarms available for laptops, and some models let you remove the hard drive and carry it with you. You also can use features like the Encrypting File System in Microsoft Windows® 2000 to mitigate the damage if someone succeeded in stealing the computer. But the only way you can know with 100% certainty that your data is safe and the hardware hasn't been tampered with is to keep the laptop on your person at all times while traveling.
Source: 10 Immutable Laws of Security