The controversial machine went online Wednesday morning, approximately 9 months after a scanner was put in place at O'Hare Airport's security checkpoint.
"This technology is important because it allows us to keep the traveling public safe, to look for items like liquids, gels that a traditional metal detector can't see," said TSA's Jim Fotenos.
Some people call the scanners virtual strip searches because the scanners produce an image more similar to an x-ray and reveals items under clothing.
"If they can take your picture and see under your clothes, if they can keep that on file and share it, I would have a problem with that," passenger said Carol Farnan.
However, the TSA says the images cannot be stored or printed.
"I think as you've seen from the images, we're using privacy algorithm. We use things to protect the privacy and security of the passengers," Fotenos said.
The TSA purchased the scanner for Midway using federal stimulus funds. So far, 464 scanners are in use at 79 airports.
The scanner is designed to screen passengers for hidden weapons and explosives. The technology uses electromagnetic waves, and the TSA says the energy emitted is only a tiny fraction of what is produced during a cell phone transmission.
Travelers who feel uncomfortable with the scan can opt for an enhanced body pat-down, but some say even those go too far.
Others believe all of it just makes the skies safer.
"I like it. If it keeps us safe, I want it," passenger Curtis O'Banner said.
"I think in today's day and age, I think it's just what we have to do with security measures. That's my mindset, and I'm not going to dwell on it," said traveler Kim Herberholt.
According to TSA, 99 percent of travelers prefer going through the body scanner to undergoing an enhanced pat-down. Most passengers faced with that choice, opt for the machine.