In computing, physical access describes any time a user can reach a computer's hardware. Conversely, logical access refers to every other type of computer use, where a user connects to a computer system without being in the same room as the machine. Though the two types of access offer some of the same features, especially in the case of remote control software, physical access grants a user far more control over a system, making it a potential security risk.
Understanding Physical Access
Most interactions with personal computers occur through physical access. Every time you use your home desktop or laptop, you do so physically -- by turning it on with the power button, typing on the keyboard and so on. In addition to regular computer use, physical access includes the ability to open the machine and remove or replace hardware components.
Types of Logical Access
Any non-physical interaction with a computer falls under the category of logical access. Many companies use logical access controls, such as passwords or biometrics, to give employees access to specific features on corporate networks without granting every employee complete control. People also utilize logical access to computers daily in their personal lives whenever they visit a website, as Web browsers allow users to access files and programs stored on remote servers. Logical access ranges from this type of limited interaction to near-complete access through remote control software.
Remote Control Software
Programs such as Windows' Remote Desktop Connection, as well as commercial alternatives including TeamViewer, GoToMyPC and LogMeIn, provide a type of logical access to computers that mimics physical access. Unlike logging in to a website, these programs allow a remote user to interact with a PC as if sitting in front of its monitor and keyboard. Some remote control programs also include features such as file transfers and presentation tools. Though these programs have security features, such as passwords and restrictions, you should only let people you trust connect to your machine through remote access -- a malicious user can very quickly damage a system when given remote control over it.
Hackers can break into a system through logical access. For example, a virus spread through an email attachment can grant its creator the ability to connect to infected computers, stealing or erasing their data. Physical access, however, poses a far greater security risk. With physical access and the right expertise, someone can completely bypass security systems on a computer, such as by using a system install disc to reset the password or attaching a keylogger. Direct access to a computer also makes it possible for a data thief to simply steal the hard drive. You don't need to regard physical computer access as a danger universally -- it's a necessity for most personal computers -- but you should restrict access to people you trust.