The field of computer security is vast. It includes aspects like disaster recovery planning, auditing, forensics and much more. We can't possibly cover all security issues in an article of a few pages. Therefore, we'll focus on practical concepts and steps you can take to make your computers and network (both home and office) more secure.
Secure your Network
A firewall should be used as a barrier between your local network and the Internet. It is a system that enforces access rules between two networks. A firewall follows strict guidelines that block or allow traffic. Specific rules are used to determine what can pass through and what can't. All businesses (and even home networks) should have some kind of firewall as a layer of protection from the unsecured Internet. Firewalls are often set up using a network router. Software based firewalls are also available for most computer operating systems (Windows, Mac, Linux).
As useful as a firewall is, it does not stop viruses that may be lurking in networks. Viruses commonly pass through firewalls via infected emails. Firewalls are also ineffective against infected portable USB devices that a user plugs into the network, nor are they effective against legitimate users whose usernames and passwords have been compromised. For these reasons, firewalls are necessary but not enough on their own.
Wikipedia hosts a handy page with a comparison of firewalls.
Secure your Desktops
Malware (malicious software) are computer programs designed to steal data, access private computers or disrupt computer operation. Common types of malware include computer viruses and spyware.
Computer viruses can wreak havoc on computer systems and networks. They can replicate themselves and spread from computer to computer. Antivirus software is the most common malware control solution but it does have limitations. Antivirus software is limited to detecting viruses that have already been discovered. It does not necessarily protect well against new viruses. This being said, installing Antivirus software and updating it regularly is crucial, especially if you are running Windows. Operating systems like Mac and Linux have a different way of managing changes to their global configurations which makes these systems less vulnerable to viruses.
A fairly comprehensive list of antivirus software can be found on Wikipedia: List of antivirus software.
Spyware is another type of malware that when installed, collects information about users without their knowledge. Spyware can collect pretty much any kind of computer data, from monitoring Internet browsing habits to collecting credit card numbers and passwords. As with viruses, spyware is generally something you don't have to worry about on Mac or Linux computers. For systems running Windows, anti-spyware software is a must. See Wikipedia's list of spyware removal tools.
Protect your Hardware
Not all security breaches are high-tech. The theft of a laptop or smartphone by a burglar can have serious consequences. Ensure that devices with sensitive information are stored safely. Encrypting data is also a good idea. When buying your next laptop, consider opting for one that uses biometric security (such as a fingerprint control) as an added layer of protection.
Company insiders are a common source of data tampering, which refers to altering or entering false data into computer systems. Often, the goal is to embezzle money. Within an organization, employees should only have access to the data they need. Your security system should ensure that once a user is authenticated, the user operates within he is or her authorized activities.
Today, wireless networks are common because of the convenience they provide. Wireless networks are also harder to protect than wireline ones. Wireless access points behind a firewall can be a backdoor into a network. Be sure to encrypt data transmissions with a wireless security scheme. Wired Equivalent Privacy (WEP) is commonly used but it is one of the least secure forms of security. Wi-Fi Protected Access (WPA and WPA2) security is a much better choice. Most wireless network hardware provides software that lets you choose between security schemes.
Protect from Unintentional Threats
Protecting from unintentional threats like human errors, computer system failures, and environmental hazards like storms and earthquakes are just as important as protecting from intentional threats like viruses. Backing up important data is an effective way of mitigating against these types of threats. Ideally, the physical location of your backups should be somewhere other than where your original data resides. Imagine your backups are in your office along with your original files and there's a fire. All could be lost.
Frequent backups are vital. The process is not as tedious as you might think, there are tools available to automate the process. Backups will speed up recovery after losses due to damage caused whether it was intentional or unintentional.
Once again, Wikipedia helps us with a nice list of free and proprietary backup software.
In the bad old days of business computing (until about 2002), securing business information and computer systems was considered to a technical issue assigned to IT (Information Technology) geeks only. Instead of taking a preemptive approach to protect ahead of threats, companies tried to clean up incidents only when they arose. IT security was considered a cost instead of a resource. A cost-based view of IT security is dangerous given the global reach of cybercriminals. Electronic fraud, malware, spyware and cyber attacks can disrupt systems, steal customer and product data, shut down e-commerce operations. The clean up of a single incident can be huge, not to mention possible legal liability and damage to the company's reputation.
Related: Protect Yourself From Internet Fraud