Virus

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Virus

Posted by ep6secuirity

Monday, May 11, 2009

Different types of Viruses

Worms

Worms are similar to viruses in that their defining characteristic is self replication. Unlike viruses, however, a worm's primary function is not to do damage to a computer, but just to keep replicating, and replicating, and replicating.

Worms also differ from viruses in that they do not require an executable file. Worms exploit security holes in computer systems or software programs. You might be thinking that simple replication without harming or removing files is not so bad, but replication can be so explosive that your computer performance slows to a crawl, your broadband connection gets clogged, and if enough computers become infected, the entire Internet can experience problems.

The worm may show up at your computer in any number of ways, most commonly via e-mail or downloading "free" software from the Internet. In this example, the worm (a virus would behave in a similar way) shows up in the form of an e-mail pretending to be pictures from a recent party. The user unknowingly double-clicks the e-mail attachment, and the worm starts executing.

When triggered, it searches your computer for e-mail addresses of your friends and family (and business associates) by dipping into your e-mail program's contacts list. The worm then e-mails itself to everyone in your list, and the replication continues.

Another type of worm requires no action by a human to spread. It simply exploits a weakness or bug in the operating system software and spreads like wildfire directly from PC to PC. Imagine this process starting out on a few hundred computers, each e-mailing 20 or 100 others, and soon enough hundreds of thousands of computers across the globe are infected. One of the most well-known worms infected more than 350,000 computers within 13 hours of release. At the peak of the spread, more than 2000 new computers were being infected every minute.

Whereas computer virus outbreaks used to be measured in days, worm outbreaks are now measured in minutes or seconds because of the speed of the Internet and ubiquitous availability of e-mail.

It is worth noting that many people (including those in the media) lump all these types of files into the virus category when many are in fact worms.

Trojan Horses

Trojan horses are probably the most unknown type of malicious program but are potentially the most devastating to those who get infected by them. Similar to viruses and worms, Trojan horses typically arrive at your computer in an e-mail attachment or as a hidden gift within a "free" software program you downloaded. Just like the horse from Homer's epic, a nasty surprise is waiting inside this gift. Trojan horses are programs that give a hacker access to your computer. After the "gift" file is opened, the hacker's program is also opened and that's when the trouble starts. Some of the more common programs are keystroke loggers and remote control programs:

Key stroke loggers collect everything you type on your keyboard (including passwords, usernames, and credit card numbers). After a certain amount of data is collected, the information is sent to the hacker (without your knowledge, of course).
Remote-control programs enable hackers to take over your machine, allowing them to go through your files and data or use your machine to attack another computer.

When triggered, the Trojan horse deposits a program onto your computer and reports back to the author, handing over the keys to access your computer.

Commonsense Approach to Computer Viruses

It is actually pretty hard to keep yourself from being infected with a virus. It is a bit like visiting a doctor's office or preschool: You can watch what you touch, who you sit near, and wash your hands, but you can still end up with a cold.

The first line of defense against computer viruses, worms, and Trojan horses is common sense. You can do some fairly simple things to prevent infection:

Do not open any e-mail (especially attachments) from people whom you do not know.
Many recent viruses replicate by sending themselves to people in your contact list, so it is possible to receive a virus e-mail from someone you know, even without that person knowing he or she sent it.
Preview any e-mail thoroughly before opening attachments. If you have any suspicion whatsoever, call the sender on the phone and ask whether he or she sent the e-mail.
Avoid "free" software, offers, and opportunities. Ask yourself why they are giving valuable stuff away.
If you use an e-mail program, such as Outlook, that gives you the option of viewing e-mails in plain text or HTML, set the default to plain text. Some viruses now take advantage of HTML and auto-launch as soon as the e-mail is opened. If you only view in plain text, any attached virus must be manually opened (which means at least you have a fighting chance).
There is also a preview pane in Outlook that does actually open the e-mail and can launch a worm or virus. You can turn the feature off for some added protection.

Very Important

If you have children who use the Internet from a computer at home, set a rule that all downloads should be approved by Mom or Dad. This is good advice for malicious software and for some topics discussed later in the book.

Unfortunately, common sense does not save you from every infection, and anyone who has been using the Internet any period of time has likely been hit with a virus or worm. We have been hit. Everyone we know has been hit, and so has pretty much every company on the Fortune 1000. So, obviously, common sense is not enough. Fortunately, we have antivirus programs that are both cheap and effective.

Labels: Virus