What is the difference between a virus and a worm?

A virus is a program written to create copies of itself, and then at some specified future time do something bad to your computer.

Viruses spread from one file to another file.

A traditional virus reproduces its own code by attaching itself to other executable files on your computer.

When the infected executable file runs or starts up, the virus copies itself.

Viruses attempt to spread throughout a computer before activating whatever malicious activity they may have been programmed to deliver.

A worm is a smarter type of virus.

A virus may rapidly infect every application on a computer or slowly infect the documents on a computer, but it cannot spread itself from one computer to another without human help.

We send email and copy files off floppy disks, and off file servers, and off the Internet.

When a user copies a file infected with a virus onto his computer, the virus starts to multiply on his computer, infecting files.

Then that user may send one of his infected files to a friend via email, and the virus spreads on the recipient's computer.

Worms are viruses that can copy themselves automatically from one computer to another over a network, like the Internet, without a human doing a thing.

This means that computer worms spread much more rapidly than traditional computer viruses.

Some worms are designed to hurt Web servers, not home computers.

The most common method for hurting a Web server is to make it so busy that legitimate users cannot access or log on to the Web sites that it hosts.

It's like having someone dialing your phone number 24 hours a day seven days a week, so your line is always ringing, and none of your friends who are trying to call you can get through.

This is essentially what the Code Red Worm does to Web servers using Microsoft IIS software.

But, says Crispin Cowan, the Chief Technology Officer of WireX Communications Inc., a company that creates software for Web servers: "The number one virus transmission method in recent years has been via exchanging Microsoft Office documents.

"This happens because MS Office documents can have macros (Visual Basic programs) attached to them."

VisualBasic or VBScript is a computer language that allows programmers and virus writers to create a list of commands that can be activated without any user interaction.

VBScript files are just plain text files with a .vbs extension, and they can be edited using any text editor, such as notepad.

They contain the set of instructions that run when a user opens the file.

Almost anything you can do while sitting at your Windows PC can be done automatically by one of these VBScript files.

Microsoft Office and Microsoft Outlook and Outlook Express can open .vbs files or scripts automatically when they open email, and .doc, .xls, and .ppt files.

So, if someone sends you a .doc file with a .vbs script attached or embedded in it, the .vbs file will start doing whatever it is it is programmed to do when you open the .doc file in Microsoft Word.

To run VisualBasic scripts (.vbs files) on your computer you must have the Windows Scripting Host (WSH) installed and turned on.

The Windows Scripting Host (WSH) is a feature of Microsoft Windows operating systems that enables .vbs files to run in Windows 95, 98, NT 4.0, and Windows 2000.

If you've have Microsoft's Internet Explorer 5 browser, you also have the Windows Scripting Host (WSH) which is the program used to interpret and run .vbs scripts.

VBScript can be disabled on your system.

"While scripting allows you to closely integrate some software, most people don't need or use it, and the VBScript allowed worms such as the ILOVEYOU virus in May, 2000 to use your copy of Outlook to send itself to all the people in your address book", explains Tom Simondi, founder of Computer Knowledge, an online training firm.

"To avoid these sorts of attacks it is best to just disable the Windows Scripting Host."

To turn off the Windows Scripting Host so that .vbs files cannot run on your computer without your knowledge, follow these instructions:

Windows 98 WSH is installed if you choose a standard installation option for Windows 98, or if you installed Internet Explorer 5, or if you download WSH from Microsoft.

1. From the Windows taskbar, select Start|Settings|Control Panel.

2. In the Control Panel window, double-click on the Add/Remove programs icon.

3. In the Add/Remove Programs window, click on the Windows Setup tab. Select Accessories and double click it.

4. In the Accessories list, find Windows Scripting Host.

5. Click on the checkbox by Windows Scripting Host to deselect it.

6. Click OK to return to the Add/Remove Program window. Then click on OK.

Windows 95, Windows 2000, and Windows NT WSH is installed if you installed Internet Explorer 5, or if you download WSH from Microsoft.

1. Right-click on the My Computer icon on your computer's desktop and select Open from the menu that appears.

2. In the My Computer window, open the View menu and select Options.

3. Click on the File Types tab.

4. Look for VBScript Script File in the list of file types (if you can't find it, your machine is safe and you don't need to do anything else).

5. Click on the Remove button. If you see a dialog asking you to confirm removal, click Yes.

Can I get a virus just from reading my email?

The short answer is that it depends on the program you use to read your email.

If you use a Windows PC and use Microsoft Outlook or Outlook Express as your email program, the answer is maybe you can get a virus just from reading your email.

To avoid getting viruses follow the instructions to turn off the Windows Scripting Host so that .vbs files cannot run on your computer without your knowledge.

If you use a Mac or if you use Eudora or Netscape or some program other than Microsoft Outlook to read your email, the answer is no; you cannot get a virus just from reading email.

You can still get viruses from other things like downloading files and from attachments that people send you when you open the attachments, so you still need to use anti-virus software regularly.

But when you just read your email you are safe from viruses.

Michelle Swartz writes every fortnight in the Personal Technology section. Enquiries should be sent to michellechristers.net