What is a Trojan Horse?

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Summer 2010 — Security News and Advice


A Trojan horse is one of the most common and dangerous types of threats that can infect your computer. Trojans are usually disguised as benign or useful software
that you download from the Internet, but they actually carry malicious code
designed to do harm—thus their name. (The name Trojan horse refers to the myth of the wooden horse that the Greeks hid in to enter the city of Troy and take it over. Just as the Greeks did, hackers use Trojans to hide malicious files in seemingly harmless files with the intent to attack or take over your machine).


There are a variety of types of Trojans, many of which can launch sophisticated and clever attacks. Here are some types to be aware of:
  • Password-stealing Trojans - These look for saved passwords on your computer and email them to the hackers. Some can even steal passwords cached in your browser history
  • Remote access Trojans - These are quite common, allowing the attacker to take control
    of your computer and access all of your files. The hacker could potentially even access your online banking and credit card sites if you have your password stored in your browser memory or on your computer
  • Destructive Trojans - These Trojans destroy and delete files from your computer
  • Anti-virus killer Trojans - These Trojans detect and kill your anti-virus and firewall programs to give the attacker easier access to your computer

A Trojan can have one or multiple destructive uses—that is what makes them so dangerous. It's also important to realise that unlike viruses, Trojans are not self-replicating and are only spread by users who mistakenly download them, usually from an email attachment.

Here are some steps you can take to avoid downloading a Trojan horse:

  • Don't open an email attachment if you don’t recognize the sender of the email
  • Don't open attachments that you do not expect to receive
  • Immediately delete emails with attachments if you do not know the sender and avoid opening an unwanted email altogether
  • Use an anti-virus program that automatically scans attachments
  • Use an email program with a built-in spam filter
  • Make sure your security software is always up to date
  • Keep current on new Internet threats so you know what to look for when you receive suspicious email

Remember that Trojans are common because they are so successful. Hackers use social engineering techniques, such as mentioning a current news topic or popular celebrity, to get you to click on their email. Just being aware of what they are and how they work can prevent you from having to deal with financial loss, identity theft, damage to your computer, and significant downtime.


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