Jan. 10, 2014 -- A Utah family who used a sperm bank more than 20 years ago uncovered a nightmare when they performed DNA tests this year: their adult daughter's real father is a convicted felon who swapped his sperm with theirs.

The family has chosen to remain anonymous but has spoken under the pseudonyms of Paula, Jeff, and Ashley to genealogist CeCe Moore about their plight.

"They came to me in October 2012... when they were interested in finding out who Ashley's biological father was," Moore told ABC News today. Moore runs an online email list and blog about genetics and geneaology. "They never imagined they'd uncover what they did."

Paula and Jeff used a Salt Lake City area fertility clinic in the 1990s to conceive Ashley, but recently performed a DNA test and found out that Ashley's real father was convicted kidnapper Thomas Lippert, who worked at the clinic in the 1980s and 1990s, they told local news station KUTV. He died in 1999.

"I felt my stomach just drop," Paula told the station. "When I called my daughter and my husband's DNA up next to one another they didn't share any DNA at all, and I just thought to myself, 'oh my God.'"

Now, the couple and Moore, along with the University of Utah, are urging families that used the Reproductive Medical Technologies Clinic to take advantage of free paternity testing to see if Lippert had any more victims. Several families have already contacted Moore and Paula through an email address they set up, Moore told ABC.

"Several said last night through email that they were clients there and were really worried. Hopefully this is an isolated case, but we just don't know," Moore said.

The University of Utah is offering free paternity tests to parents who used the sperm bank during those years.

"The bottom line is that we are hoping that couples who used the Reproductive Medical Technologies Clinic in Salt Lake City (which they, like Paula, may have simply known as the University of Utah's fertility clinic) to conceive between 1986 and 1995 will hear about this story and reach out to Paula," Moore said in a blog post on her website this week.

"If couples suspect that they may have been one of Tom's victims, they are encouraged to have their children tested...," she wrote.

Paula told KUTV she believes Lippert's actions were purposeful. He kept a stack of baby photos at the desk of the clinic that he showed off as babies he "helped" to conceive, she recalled.

"I just thought, 'oh my gosh,' this was not an accident, this was intentional. All those photos of the babies that he was so proud of I thought, 'oh my god how many of those are his biological children?'" Paula told KUTV.

The clinic, which is now defunct, was associated with the University of Utah. According to the university, it was a privately-owned clinic that did some work for the school, but was also owned in part by three faculty and staff members.

"Since April 2013, the University of Utah has been investigating credible information regarding the possible mislabeling or tampering of a semen sample," the university said in a statement, referencing the plight of Paula, Jeff, and Ashley.

"There are no remaining records from RMTI to prove the claim and the man in question has been deceased since 1999. Consequently, it is unknown how this incident might have happened. In addition, there is no evidence to indicate this situation extends beyond the case in question," they said.

Moore did not immediately return requests for comment from ABC News.

If you want to ask about the free DNA tests, you can contact the facility by clicking here.