2.4 WORM

 A worm shares many characteristics with a virus. The most important characteristic is that worm is self replicating too. Worms seek to infect and replicate without targeting and infecting specific files already present on a computer. . The two most common ways a worm can spread are through email and security flaws in computers connected to a network or the Internet.

If a virus infects a legitimate file, the virus code can be cleaned out and removed. But this is not the case with worms. Worms generally create and occupy the files that contain their code without using or involving any real data or binary files, the normal cleanup technique for worms is to delete all infected emails or messages that provide their containers.

Worms which use email to spread are known as massmailing worms and are typically written in a variant of the Visual Basic programming language. They usually exploit the Microsoft Outlook or Outlook Express emailing programs on Windows. Typically, the worm checks a user's Outlook or Outlook Express address book for a list of stored email addresses and then the worm sends a copy of itself to each address. Massmailing worms can spread particularly quickly since they tend to come from someone that the victim knows. The recipient is likely to read the email and accidentally help the worm spread to their own address book of email addresses. Massmailing worms most often target Microsoft Windows users running Microsoft Outlook or Outlook Express, because those are the most common operating systems and email programs.

Thus, one way to protect you against a massmailing worm is to either use a different operating system (such as Linux or the Mac OS) or use a different email program. Internet worms, in contrast, spread by searching the Internet for a computer running a specific type of operating system or webserver with a known flaw in it. Once the worm finds a vulnerable computer, the worm copies itself to that computer through the known flaw and then proceeds to use that computer to look for other targets to attack.

Sometimes the mere existence of a worm mass mailing or copying itself across the Internet can cause your computer to slow down or even crash without the worm deliberately trying to harm your computer. Other times the worm may include a payload that wipes out data, infects your computer with a virus, or retrieves documents at random from your hard disk (which could include sensitive business or highly personal documents) before mass mailing them to everyone listed in your Microsoft Outlook or Outlook Express address book.

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