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After outing several major retailers for their filthy practice of putting soiled undies back on the shelves, NBC's "Today" show recently returned to the stores in its ongoing "Secret Filth Exposed" series.

The good news? The investigative team found that each store that had been caught re-selling returned, deliberately soiled garments has since cleaned up its act.

The too-gross-for-words news? A whole new group of retailers -- including Walmart and Marshalls -- was caught returning questionable intimates to the sales floor.

The "Today" show's Jeff Rossen first reported on this dirty little retail secret in March, when secret shoppers were sent to J.Crew, Saks Fifth Avenue, Gap, Victoria's Secret, Nordstrom, Bloomingdale's, and Macy's.

The news team removed price tags and hygienic strips from panties, stained them with baby oil, and marked tags with two black dots for identification purposes. All of the stores accepted the soiled returns, and the show's investigators found the merchandise back on the shelves at Gap, Victoria's Secret, Macy's, Nordstrom, and Bloomingdale's. A Victoria's Secret whistle-blower told Rossen it was common practice to put returned panties back on sale. Fortunately, the stained undergarments were not found at J.Crew or Saks.

A microbiologist who has worked with "Today" explained that soiled undergarments can harbor bacteria and viruses for several weeks, with the most imminent danger coming from "fecal material."

The offending retailers all put out strong statements condemning what "Today" found and vowed to reeducate their sales teams, adding that what happened was not store practice. Some noted that they have generous return policies, and while customers may have legitimate reasons for returning worn garments, they should never have been put out for sale.

To see if they were true to their word, "Today" went back to the retailers, this time at an upscale suburban New York mall instead of New Jersey, where the original returns and purchases took place. Some stores outright refused the returns, pointing out that the panties had been worn. Nordstrom did accept the underwear, but "Today" watched a clerk seal it in a plastic bag and never saw it back on the shelves.

Still, "Today" found other retailers engaging in the highly questionable practice. They did the black dot/baby oil test on swimwear and underwear from Walmart, JCPenney, Target, and Marshalls. Target and JCPenney accepted the returns, but investigators did not find the merchandise on the racks. Unfortunately, the garments were back on the sales floor at Marshalls and Walmart.

Again, the newly identified retailers condemned what "Today" found and insisted it was not in keeping with their policies on undergarments or swimwear. They, too, vowed to prohibit the practice and stress the matter with employees.

"Today" show host Matt Lauer summed it up by saying this is a cautionary tale for shoppers: "The lesson here is if you buy, wash before you wear."

Here at StyleList, we will be packing hand sanitizer the next time we stock up at one of those semiannual intimates sales.

Meanwhile, in other disgusting news, read about the "Good Morning America" report on how new clothes can make you sick.