Computer users, particularly those relying on Microsoft Windows software, can take a number of steps to guard against online menaces such as hackers, viruses and spyware.

* Install a firewall.

Programs such as ZoneAlarm ward off hackers and certain types of spyware and adware. They allow you to close certain online entrances, or ports, to your computer that you don't use regularly. They also alert you to unauthorized attempts to access your system.

A router, a device that allows more than one computer to share an Internet connection, can provide an additional layer of protection. Outside Internet traffic "sees" the router, not the computers that are connected to it, making them more difficult to target.

* Install and update antivirus software.

Software from McAfee, Symantec and other companies identify and delete viruses and other programs that can damage hard drives, send unauthorized e-mail or take over machines to perform other tasks.

* Use anti-spyware software.

Ad-aware, Spybot Search and Destroy, Spy Sweeper and other programs identify and delete programs that track user activity or serve ads.

* Protect e-mail with spam filters.

This software blocks unsolicited e-mail messages and those that might harbor viruses or other trouble.

* Download software updates.

These are patches that fix vulnerabilities in recent releases of products such as Microsoft Windows or Internet Explorer.

* Other precautions.

Some computer experts recommend using non-Microsoft operating systems such as Mac or Linux. Hackers and other mischief-makers have been less aggressive about targeting computers running those systems. Windows users can also insulate themselves from some problems by using a non-Microsoft browser, such as the free Mozilla Firefox.