Computer Security: How to reduce your chances of getting a virus or Trojan horse

Short of unplugging your computer, it's hard to guarantee that you won't run into a virus or trojan horse, but if you're careful, you can significantly reduce the chances of this happening.  Here are the steps that I use at work and at home.

Recommendation 1: Install antivirus software on your machine and keep the virus definitions reasonably up to date.  Consider turning on automatic scanning (I don't do this because I don't want to take the performance hit, but if you are using your computer mainly for email and web access, then you shouldn't see much of a performance penalty).

Recommendation 2: Practice safe surfing.  Don't visit sites that have a higher likelihood of giving you a virus.  This includes sites that provide illegal (pirated) intellectual material, such as software, registration keys, music, images, etc.  Use caution when downloading programs.  Before downloaded, check the publisher's site to see ifi the company looks legitimate.  Download directly from the publisher's site, if possible, or a site recommended by the publisher.  Scan software with an antivirus program before installing it and after installing it (if you have automatic scanning enabled, then this step should not be necessary).

Recommendation 3: Use Web-based email, such as Yahoo or Hotmail.  Email is one of the primary ways in which viruses are transmitted.  With Web-based email, mail and attachments are not automatically downloaded to your machine.  Yahoo provides automatic scanning of downloads, so the only risk with Web-based email is HTML-based viruses.  If you are wedded to your mail program, then make sure that your antivirus program is properly configured to scan all incoming mail.

Recommendation 4: Don't use Internet Explorer.  It's a solid piece of software, but given Microsoft's huge share of the market, most of the effort in finding security holes is aimed at IE.  Two other popular browsers are Opera and Netscape/Mozilla.  I switched to Phoenix, a Mozilla variant, several months ago, and I've been pleased with it.  If you do switch, you should still keep IE around (not that Microsoft makes it easy to remove) because there will be always be some sites which just don't work correctly.

Recommendation 6: Install a firewall.  I recommend a software firewall for all computers that are ever connected to the internet.  For broadband always-on connections, I also recommend using a hardwire firewall.  Hardware firewalls, properly configured, will make it difficult for intruders to access your machine.  Software firewalls provide a similar capability, but also help protect against trojan horses by allowing you to decide which programs on your machine can access the internet.

Definitions:

A virus is a program that will infect your computer.  It may be benign (for example, it could just display a message) or it could damage your computer (by destroying files or disk partitions).  The well-known antivirus programs are reasonably good at keeping your machine virus-free

A Trojan horse is a program that allows others access to your computer.  It can either send information (such as files, personal data, etc.) out, or it can allow a remote hacker or program to take control of your computer (as an end in itself, or as a stepping stone for hacking into other computers or performing a distributed denial-of-service attack).

Antivirus programs don't always detect Trojan and viruses because there is sometimes a debate about whether something really falls into these categories.  Two examples: