(FORTUNE Magazine) – Melissa, PoizonBox, Code Red, Slammer, MyDoom--it's nasty and brutish out there in cyberspace. Viruses and worms are every- where. How can you make sure you have the proper defense? Here are steps to take if you're an individual or a small business:

1. Install an antivirus program. Symantec makes the most popular one, Norton AntiVirus. But there are plenty of other choices. Try McAfee, Sophos, TrendMicro, or Panda Software. These companies all offer personal firewalls too; make sure your computer has one. (Zone Labs' ZoneAlarm is a popular choice.) If you are a Windows XP user, make sure the built-in firewall is switched on.

2. Check for patches or software updates. If you barely touch your computer and e-mail only every couple of days, once a month should be fine. Otherwise, update software more frequently, either manually by visiting the website of your operating-system supplier, or by setting your PC to do this automatically. The downside is that sometimes patches carry their own virus. A patch for the Sasser worm spawned Netsky, which did even more damage. Oh, and don't forget that your antivirus software needs regular updating too.

3. Be alert. When retrieving an e-mail, make sure you know who it's from. When you visit websites, be careful where you click. Carelessness leaves you vulnerable to "phishing," one of the scariest scams around. Essentially, evildoers set up a website that looks just like your bank's homepage or your favorite e-commerce site. You are asked to enter your login and password or financial information, enabling the phisher to steal your money. Don't fall for it. If you get an e-mail that appears to be from your bank, triple-check to make sure that it is. Rather than click on an embedded link, go to the bank's main page first, or call customer service to verify that the bank has indeed sent the e-mail. -- Christine Y. Chen