Downloading from Web sites

Viewing Web sites is fairly safe, though there are a few viruses that can infect your machine directly from a Web page. Read about them here.

Downloading pictures and text from Web sites is relatively safe (though you might be breaking copyright law) but do remember that clever virus makers have worked out how to give their viruses the same file extensions as harmless pictures. Be wary of any picture that does not open automatically, but instead expects you to click on its name to open it.

Bigger problems arise when you download executable files, for example software, including games. Anything that runs as a separate program or needs some kind of installation procedure is usually an executable and needs to be dealt with carefully.

Executables get direct access to the core of your computer. You'd be surprised how easy is to write an executable that destroys your computer in a few seconds. It's also relatively easy to disguise it so virus protection programs don't know if it's malicious or not - all they know is that they don't understand it.

Whenever you download and run software from the Internet, you're running a risk of downloading a nasty executable. That's why companies such as banks don't allow their employees to do it.

You only have one real safeguard, which is the good reputation of the site you're downloading from. Big software companies and the major download sites such as Tucows, Slaughterhouse, Downloads.com and ZDNet make sure they don't include nasty stuff in their programs. Their reputations are worth millions of dollars and they don't want the risk of bad publicity. Sure, something slips through from time to time, but the amount is negligible.

You face bigger problems when deciding whether to take a download from an unknown site. Then it's down to personal judgment. Do they seem honest? Do you have any reason to distrust them? Would you be prepared to physically hand over your computer to these people and let them install something on it? That's effectively what you're about to do.

A classic con is offered by some very seedy pornography sites, often from the Eastern Bloc. They offer specialist viewing software. If you install this, it changes your Internet dial-up settings and your computer begins to call premium rate phone numbers in exotic locations. It may even change your standard Internet call up to one of these locations. People have been stung for thousands of dollars this way.

Here's another aspect of running executables - you may not even know you're doing it. It's relatively easy to disguise an executable as something else. The icon can be disguised, and on Windows you don't see the file extension .exe unless you're gone through the complicated process of making it visible. So something that looks like a Word document or maybe even a text file, could actually be an executable. It happens.

Many downloads are in Zip format. A Zip file is a set of ordinary files that have been compressed to travel down the wire faster. The files within a Zip file can hold viruses in the same way as any other file. Receiving zipped files makes things marginally harder for your Virus protection program, though most of them can deal with it these days. If your virus checker can cope, then there's not much difference between downloading a Zip file and any other file.

One thing to watch out for is malicious .exe files disguised as Zip files. It's a favourite method of disguising them, because nobody thinks twice about double clicking a Zip file to open it. The only way you can spot these is to display file extensions and read them.

An introduction to viruses

Email and attachments

Displaying file extensions

Anti-virus software

Assess your risk

In Microsoft Word documents