A computer programmer who created malware used to hack the Democratic National Committee during the 2016 U.S. presidential race has become a cooperating witness in the FBI's investigation into the historic DNC breach, according to The New York Times.

The man, identified only by his alias, "Profexer," turned himself in to Ukrainian authorities earlier this year and has since been made available to FBI agents investigating the historic hack, The Times reported Wednesday.

He's credited with creating a piece of malware called a PAS web shell used by the DNC hackers to discretely execute commands on hijacked computers, but hasn't been arrested because he only wrote the tool and doesn't appear to have been involved in the actual breach, Ukrainian police told the newspaper.

He distributed his malware online for free, but also took donations from customers seeking specialized hacking tools or requiring assistance, the report said. He stopped offering those services in January shortly after the Department of Homeland Security identified his PAS shell in a technical report detailing the DNC breach, however, and has since become a witness in the FBI's investigation.

"He told us he didn't create it to be used in the way it was," Serhiy Demediuk, the chief of the Ukrainian Cyber Police, told he Times.

The U.S. has blamed Russian state-sponsored hackers with breaching the DNC and other targets affiliated with Hillary Clinton's unsuccessfully 2016 White House campaign during the course of conducting an operation meant to help her Republican opponent Donald Trump and disrupt the U.S. election process.

The nature and extent of the conversations "Profexer" had with his customers was not clear, and a member of the Ukrainian Parliament, Anton Gerashchenko, said the programmer was unaware that his malware would be used against the DNC until after the fact, The Times reported.

"Profexer" has been made available to U.S. authorities, Mr. Demediuk said, and the FBI has posted a full-time cybersecurity expert at its embassy in Kiev, The times reported.

The FBI declined to comment, the report said.

Russia has previously denied meddling in the U.S. election.