A network is a communications system in which several computers are linked. This enables them to share resources, like software, hardware and data.

• Local Area Networks (LANs) consist of a number of computers covering a relatively small area, for example a single office or a school.
• Wide Area Networks (WANs) cover a much larger area and may consist of a number of linked LANs. They may cover an entire country. Automatic transfer machines (cash machines) are linked by a WAN.

WANs are often connected together using the Internet. The advantages of having access to a network include the following:

• Resources can be shared, so that expensive software and vast databases can be accessed from each individual PC.
• Several computers can make use of the same printer.
• Network users can communicate with each other using email or instant messages.
• Large databases can be updated by a number of people at any one time. Users can benefit from this new information almost instantly.
• Shared data can be backed up efficiently using one file server.

Disadvantages include the fact that:

• Managing networks requires specialist knowledge and training.
• Network cabling and file servers are expensive.
• Viruses can infect a number of computers on the same network.
• WANs can be vulnerable to hacking.

Encryption is sometimes required when information of a sensitive nature is being transmitted. If you were to pay for online goods using your credit card details, for example, your details may be vulnerable to misuse. Encryption scrambles your details so that they can only be understood by a recognised trader who holds the key or descrambling software.