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A Trojan is a form of malware disguised as legitimate software. It is often employed by cybercriminals to steal private data, spy on users and gain unauthorized access to systems. If you've been paying attention to computer and Internet security at all over the past decade, you've undoubtedly come across the phrase "Trojan virus." While you may know that these pieces of malware are bad news, you may not be aware of just what they can do to your computer, how they get into your machine, and how to avoid them. By gaining a complete understanding of what a Trojan is and what it can do, you put yourself in the best possible position to avoid dealing with these dangerous pieces of software altogether.

What is a Trojan Virus?

The term "Trojan virus" is a bit of a misnomer, but it's commonly used instead of the more correct term, "Trojan." A virus will infect regular computer files, taking over a specified file and corrupting it in the process. The virus will then attempt to propagate itself to other computers by infecting other files.
In contrast, Trojans are programs in and of themselves, as they don't need to corrupt another file to do their dirty work. They also don't propagate themselves to other computers, infecting only one machine per instance. But don't let this fool you; the worst Trojans are as damaging as any computer virus.

How Trojans Work

Just like the story of the Trojan Horse from antiquity, the Trojan malware appears to be something that you want. It often takes the form of a piece of free software or an attachment in an email, and then once you give it permission to install on your machine, it opens up the floodgates.

Once the Trojan has access to your computer, it can do just about anything, but the majority of these types of malware look to gain complete control of your PC. This means that anything you do on the computer gets recorded and sent to a server specified by the Trojan. This can be especially dangerous if you use your PC for financial transactions, as the Trojan will send your credit card or banking information to people looking to either use it or sell it. Trojans can also be used to turn your computer into a zombie, allowing the hacker to use your computer and Internet connection to launch cyberattacks around the world.

How to Protect Yourself

Trojans are so named because they need your permission to run on your computer, either when you run the program yourself, or if you open a document or image that then runs the program. With this in mind, the first and best defense against Trojans is to never open an email attachment or run a program when you aren't 100 percent certain of the source, which includes all files downloaded from peer-to-peer programs or websites. But this is rarely possible in today's interconnected world, so a few more specific security measures are called for.

Always keep your software up to date. This goes doubly true for important programs like your operating system and browser. Hackers exploit known security holes in these types of programs that can help the Trojan do its work, and even if the vendor patches the holes, it won't do you any good unless you maintain the latest version of your software. To keep your Internet connection as secure as possible, always keep a firewall up. Both software and hardware firewalls are excellent at controlling malicious Internet traffic, and can often stop Trojans from downloading to your computer in the first place.

All these things are helpful, but to really be secure you have to install an antivirus software or Trojan remover. This software, when kept up to date, will scan your system to make sure you haven't downloaded a Trojan, and will automatically scan any program or file you execute to ensure its safety. There are free Trojan removers on the Internet, but few are regularly updated and some are even Trojans themselves. To best protect your computer, go with a brand-name antivirus software with a free trial. This will allow you to see the benefits of such a program before you actually purchase it. These programs often come as part of an overall security package, but allow you to specify what kind of protections you need and disable other features.

Keeping your computer safe from Trojans doesn't have to be a monumental task. By following a few simple rules about Internet safety and coupling those rules with a robust security solution, you can rest assured that your computer is safe from the vast majority of Trojans and other malware that's out there.

Avoiding a Trojan Virus: Keeping the Gates Closed

Trojans are a type of malware disguised as legitimate software. Learn the risks and how to protect yourself here.
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