DENVER -- An exclusive 7NEWS investigation takes you inside your computer to show how a few common decisions can endanger your most critical information and the life of your computer.

Evidence of this can be seen inside a so-called "computer emergency room" a place where technicians diagnose problems and examine the cause of a computer meltdown.

"If you surf the Internet, you are going to get something," said computer technician Nicholas Sawlidi.

"The client was looking for free music, typed in on a web search looking for free music, downloaded a couple programs. All of a sudden, tons of pop ups are happening, computer slowness," said computer technician Fred Deichler.

So how does a computer go from the box to a technician's bench?

Jim Tanner, one of the country's leading forensic computer examiners, worked with 7NEWS to see what happens when we plug in a brand new computer and use a basic Internet connection.

"I will be using forensic software to examine the computer. It's the same software all the law enforcement agencies use -- the FBI, CIA, we all use the same software," Tanner said.

Then we watch how quickly and how easily our computer can become their computer.

"You can lose control of your computer and, in fact, someone who is sophisticated can turn your computer into a server for their porn site without you knowing it. That's the danger," said Tanner.

We connected the computer to three popular filesharing sites -- locations popular with teenagers for downloading free music, pictures and videos.

"Our computer is talking to about 15 different countries," said Tanner.

We logged onto Kazaa, Bit Torrent and Limewire and downloaded their free software, opening the door to a worldwide network of file sharing.

"We will be able to see people coming into our system. I've got software running that monitors every single packet sent or received by this computer," said Tanner.

With our firewall in place and our antivirus running and up to date, we passively stayed connected to the three peer-to-peer networks for six days -- never touching the keyboard and never searching for or sending a single file.

Using forensic software, Tanner discovered 538 suspect files on our computer.

"The average person would never see these things occurring," said Tanner.

In the next phase of our investigation, we weakened the firewall and the antivirus, a common and often hidden vulnerability caused by expired and outdated software or clicking on deceptive popups.

"It appears at this moment that somebody else is in control of this computer and not me," Tanner said.

This time, in just 13 hours, we lost control of the computer's Internet access.

"They're using our system to move information all over the world," Tanner said.

Again our activity was totally passive. We never touched the keyboard and never searched for or sent a single file.

"I am not sure how exactly this machine has been hijacked," said Tanner.

An overnight forensic analysis found an additional 107 suspect files.

One of the suspect files was loaded when we downloaded the file sharing software and was never detected by the computer's antivirus scan.

"That's the one that concerns me the most," Tanner said. "This is a very spooky piece of software. There's a great big question mark around it."

It's a piece of hidden software, only discovered with a deeper forensic analysis, which gave its owner remote access to our computer.

"If that element is turned on, this computer becomes part of that company's network," said Tanner.

Ultimately, three file sharing programs, 13 hours on the Internet and contact from computer users in 45 different countries transformed a brand new out-of-the-box computer into a potential tool for unknown predators.

"I think it's both a warning and a wakeup call. It's a warning that installing software that you don't fully understand can be very dangerous. It's a wake up call that if your computer isn't adequately protected, you can get in big trouble fast," said Tanner.

Protecting your computer is critical. Tanner suggested installing a good antivirus package and regularly keeping it up to date, installing a good anti-spyware package and scanning your system weekly, and installing a dependable firewall to protect your key information.

Resources:

• Tips To Protect Your Computer
• Tips Protect Kids Online
• Where To Get Free Firewalls, Security Tests