Worms, Viruses, and RATs - What's the difference?

The basic difference between a worm, a virus, and a RAT is that a viral infection requires an action on the part of the recipient to spread, a worm doesn't, and a RAT opens a doorway into your computer for hackers.

Where does a virus come from and what does it do?

Viruses can be picked up virtually anywhere on the Internet.  They are embedded in web sites, in emails, ad banners, MP3 downloads, video downloads, shareware, and forms.  Some virus have been intentionally programmed by the author; but some bad guys go around embedding viruses without the author's knowledge.

A virus adds itself, its code, to your system in such a way that you don't know about it, but every time you use that system the virus activates and spreads.

The virus can attach itself to your boot so that it activates each time you start up your computer.  It can attach itself to a file or program, application file or script. 

A virus may not actually do anything.  Some just sit there, replicating for no particular purpose, installed on your computer by an idiot who is pleased with himself for no other reason than the fact that he could do it without you knowing about it.  This is a so-called harmless virus.

The problem is that when a "harmless" virus attaches itself to an environment it was not designed for, it gets confused and becomes destructive.

Other viruses are designed to be destructive from the outset and run around altering programs and causing subtle but cumulative havoc.  In other words, you may not notice anything at all for a few weeks, then a little something doesn't work right here and a program component won't come up there.  After a while, nothing works right because each time you pull up and use an infected file or program the virus activates and spreads itself to another component on your computer. 

Or, the virus may simply crash your computer.

Your only real defense against this type of attack is a good anti-virus program.

What is a worm?

A worm may also be called a virus, but coded in such a way that it doesn't require an action on the part of the computer owner to do it's thing.  It's self-replicating and can be designed to do any number of things such as delete files, infect emails, open a backdoor, and cause general mayhem.  Because it multiplies, it can cause a huge overload on your computer.   You will notice your computer getting slower and slower until it just stops working altogether.

Again, a good anti-virus program is your best solution for preventing worms from invading your computer.

What is a RAT?

Another virus-type infection, a RAT is specifically designed to open a backdoor to your computer.  It breaches your firewall and allows entrance to hackers who can literally do anything on your computer that you can do, plus a lot of stuff you may not know you can do.  For instance, since most everything you do on the Internet is cached on your hard drive, the hacker can pick up the credit card numbers you used to make online purchases, your social security number if you used that to file your income taxes online, the password and user name to access your online banking, your email address book, and so forth.

Your best defense against this type of infection is Internet tracks removal software.

Removing a virus can cause more damage than the virus itself

It's often very difficult to determine exactly what has been infected.  Removing a file or a program that is obviously infected because it no longer works properly doesn't mean you've actually removed the whole infection.  Nor is it safe to remove files and folders because they may be vital to your computer functions, causing your computer to crash.. 

The best way to remove a virus is to let an anti-virus program like AVG Anti-Virus do the job, and do it right. 

Some images on this page were obtained from Garry Lab's Big Picture Book of Viruses.