There was a time when computers were extremely vulnerable to viruses.

Somewhere around 2005, plus or minus a couple years, Microsoft closed most of the holes in Windows.

Today, as long as you keep Windows up-to-date, and you use the default security settings, you should not get anything bad on your computer, if you do not do anything overtly foolish or naive.

To get something bad on your computer, you have to install it yourself, usually by being tricked.

These are the ways you are likely to be tricked. Here is what to watch out for.

1. Email zip attachments.

In Outlook, you can click on any email attachment safely, including zip attachments.

However, programs can be included inside zip attachments.

Once you open up a zip attachment, do not click on any programs inside, unless you specifically asked someone to send you that program.

Be especially wary of zip attachments sent to you from your boss and your customers. These are the ones you are most likely to open by mistake.

2. Other attachment files with macros.

Excel spreadsheets and other attachments that can run programs can harm your computer.

When you open these, they tell you that macros are disabled by default. If you turn on macros, you put your computer at risk. Only turn on macros if you know the source is safe.

3. Websites that say your computer is infected.

Websites cannot run programs on your computer unless you click OK when asked if you want to run something. Unless you trust a website, do not run any programs from it.

Websites that say your computer is infected are trying to trick you. Do not run programs from them, unless you know the website is legitimate.

Windows XP has closed external holes, but if you did do something foolish and installed a virus, the virus can do bad things to your computer.

Starting with Windows Vista and improving with Windows 7, Microsoft has added internal controls. Windows restricts programs to certain areas of your computer. When a program tries to do something unsafe, Windows blocks the program and asks for your approval. So, if you do accidentally install a virus, you have further protections.

By Andrew Weitzen (c) 2010

Weitzen is the publisher of several online Internet journals including: InternetHandholding.com, DomainNames.gs, DotNetNuke.bz, Programmer.bz, Software.vg, WebHosting.vg