Or somebody could crash your computer or erase your programs. Get a good anti-virus program and have it scan your computer each week. If you have a Microsoft computer, turn off the file-sharing function. Don't run a program or open an e-mail attachment without first running a virus scan. Then there are firewalls, which monitor your Internet connection and refuse to let anything suspicious into your computer.
Firewalls come in hardware and software varieties.
Hardware firewalls are boxes that you plug your computer into. Many broadband routers and modems now come with built-in firewall protection. Software firewalls, like BlackICE Defender, are programs that you download from the Internet to your personal computer.