More than 200,000 computer users in some 150 countries have been affected by the so-called "WannaCry" ransomware attack, a rapidly spreading virus that has impacted major corporations and hospitals.

"We have never seen a cyber attack with this kind of breadth," said former CIA director Michael Morell. "It spread very rapidly, and that is very unusual and very frightening."

The malicious code encrypts a user's files, making them no longer readable.

The hackers then demand a $300 ransom to decode the data or the files will be permanently deleted.

"Like any ransom situation, just because you pay doesn't mean you will be satisfied with the outcome," said University of Houston computer security professor Chris Bronk. "This is organized crime."

He says some victims have had no other choice but to pay and hope they can get their files restored.

Bronk says the best defense is to keep your computer updated and back up your important data.

Houston dentist Dr. Zeb Poindexter knows the pain of a ransomware attack all too well --- his office was hit right before Christmas.

"The cyber-attack came in and we didn't know what was going on," said Poindexter. "You couldn’t access files. You couldn’t check x-rays through digital systems. Everything digital was locked down."

Poindexter had important data backed up on a server that was outside of his office, something he recommends every business owner should do.

The second-generation dentist also says he believes in keeping hard copies of important records just in case computer systems go down, a habit that he says helped him get back to business.

"I'm old school," said Poindexter. "There's an old saying, 'the more complicated you make the plumbing, the easier it is to stop it up,' we have to use common sense against these criminals.' "