This tip for the new year is old news: don't let strangers run programs on your computer.

Virus and "malware" writers are endlessly inventive. They're always working to find new clever ways to trick people into installing their programs on your computer. Once you've installed a virus or trojan program, they have control of your computer and can use it to send spam, launder money for criminals, or participate in attacks against web sites.

Why would they want to use someone's computer to attack a web site? One computer alone can't do much, but if the bad guys can rope together a lot of them, say 10,000 or 100,000 PCs, they can overwhelm a web site and extort money from the owners to lay off. These techniques have even been used in attempts to topple governments by shutting down a whole country's communications infrastructure (as in the 2007 cyber attacks on Estonia). You are probably already running anti-virus software, and that is an essential first step. But it's not sufficient by itself. When the bad guys find a new exploitable bug, they may put it to use before the anti-virus software can be updated to catch that problem. Security software always has to pla catch-up with the bad guys. So, adding a little vigilance on your part can go a long way to helping keep your syste free of malware. Which brings us to our tip.

Recently the bad guys have found ways to exploit how web browsers display messages to  the user. Here’s how it works: you receive a mail message with a very convincing subject line that makes you want to look at a particular video. You follow the link to the video and your browser tells you that you need to install a new or updated Flash plugin  to view the video. That's not an unusual request, so you click the button to install the plugin. But the bad guy has directed you to
another site and  those clicks just enabled them to install a malicious program instead of the updated Flash
plugin.

Game over.

How do you prevent this?

There are a few red flags in this scenario:
1. Don't follow links in emails sent to you by someone you don't know. (This tip breaks down if the bad guy successfully impersonates someone you know or think you might know).

2. When a pop-up tells you that you need a new version of the plugin, don't follow the link provided there. Rather, try to get info about what plugin is needed, and go to the web site of the maker of that plugin to download it directly (for example, Flash is made by Adobe, www.adobe.com ). If you don't know
who makes the plugin, go to the website for your browser.

3. Remember that any time you install a program on your computer, you give that program permission to take over your computer. If you're not sure where the program came from, step back and think twice before clicking "OK". This extra bit of diligence will help keep you and your PC safe.