Email viruses

Many of the most prolifi c viruses distribute themselves automatically by email.

Typically, email-aware viruses depend on the user double-clicking on an attachment. This runs the malicious code, which will then mail itself to other people from that computer. The Netsky virus, for example, searches the computer for fi les that may contain email addresses, and then uses the email client on your computer to send itself to those addresses. Some viruses, like Sobig-F, don’t even need to use your email client; they include their own “SMTP engine” for constructing and sending the email messages.

Any attachment that you receive by email could carry a virus; and launching such an attachment can infect your computer.

Even an attachment that appears to be a safe type of fi le, e.g. a fi le with a .txt extension, can pose a threat. That fi le may be a malicious VBS script with the real fi le type (.vbs) hidden from view.

Some viruses, such as Kakworm and Bubbleboy, can infect users as soon as they read email, exploiting a vulnerability in the operating system or mail program. They look like any other message but contain a hidden script that runs as soon as you open the email, or even look at it in the preview pane (as long as you are using Outlook with the right version of Internet Explorer). This script can change system settings and send the virus to other users via email.

Email viruses may compromise your computer’s security or steal data, but their most common effect is to create excessive email traffi c and crash servers.

To avoid email viruses, you should run anti-virus software and avoid clicking on unexpected attachments. You should also install the patches issued by software vendors, as these can close down the vulnerabilities exploited by email viruses.