What is a computer virus?

A computer virus or worm is a self-replicating program that can spread by email or by inserting copies of itself into other programs or documents. Most viruses or worms are malicious programs designed to infect and gain control over a computer without the owner’s knowledge.

Viruses spread via email can knock out systems burdened by the enormous amounts of generated email, and cause major headaches for individual users.

Virus epidemics mostly infect Microsoft Windows systems due to their popularity, and usually through email programs such as Microsoft Outlook. This is because such email clients can open and execute programs that are sent as email attachments.

By using a web-based email program such as the Runbox Webmail, automatic execution of possible viruses is prevented before they reach your computer. It also strips any malicious scripts from messages so they can’t infect your computer (unless you manually open the original message in a separate window).

How to avoid email viruses and worms

Here are some simple rules you can follow to avoid being infected by viruses through email.


  1. Use a professional and dedicated email service such as Runbox with strong virus filtering. Subscription services often provide higher levels of security and support.
  2. Make sure that your Runbox virus filter is activated.
  3. Use the Webmail interface at www.runbox.com to read your email, as it will never open an attachment by itself.
  4. Don’t download all your email to an email client unseen. Screen your email first, and delete suspicious-looking and unwanted messages before downloading the legitimate email to your local email client.
  5. Make sure your computer has updated anti-virus software running on it. Automatic updates are essential for effective virus protection. Combined with server side scanning, you now have two layers of security.
  6. Disable message preview in your email client, especially on Windows platforms. Otherwise, malicious programs attached to incoming messages may execute automatically and infect your computer.
  7. Ignore or delete messages with attachments appearing to be sent from official Runbox email addresses. We practically never send email with attachments to our customers, so if you receive such an email it could be falsified.
  8. Take caution when opening graphics and media attachments, as viruses can be disguised as such files.
  9. Maintain several independent email accounts. If a virus infects your only business email address, you’ll be in trouble. Also, keep backups of your most important email and files separately.


  1. Do not open an email attachment unless you were expecting it and know whom it’s from.
  2. Do not open any unsolicited executable files, documents, spreadsheets, etc.
  3. Avoid downloading executables or documents from the internet, as these are often used to spread viruses.
  4. Never open files with a double file extension, e.g. filename.txt.vbs. This is a typical sign of a virus program.
  5. Do not send or forward any files that you haven’t virus-checked first.

Viruses and spam

Virus-makers and spammers often cooperate in devious schemes to send as much spam as possible as efficiently as possible. They create viruses that infect vulnerable computers around the world and turn them into spam-generating “robots“. The infected computers then send massive amounts of spam, unbeknownst to the computer owner.

Such virus-generated email is often forged to appear to be sent from legitimate addresses collected from address books on infected computers. The viruses also use such data, combined with lists of common (user)names, to send spam to huge numbers of recipients. Many of those messages will be returned as undeliverable, and arrive in innocent and unknowing email users’ Inboxes. If this happens to you, use the trainable spam filter to catch those messages.

See also What is spam, and how to avoid it? for more information about spam.