The editor-in-chief of Newsweek confirmed Friday that the magazine’s website was on the receiving end of a denial-of-service attack Thursday night, following the publication of a story accusing one of Donald Trump’s companies of violating the Cuban trade embargo.

Editor-In-Chief Jim Impoco noted that the attack came as the story earned national attention.

“Last night we were on the receiving end of what our IT chief called a ‘massive’ DoS (denial of service) attack,” Impoco wrote in an email to TPM. “The site was down most of last evening, at a time when Kurt Eichenwald’s story detailing how Donald Trump’s company broke the law by violating the U.S. trade embargo against Cuba was being covered extensively by prominent cable news programs. Our IT team is still investigating the hack.”

Later Friday afternoon, Impoco emailed TPM that in an initial investigation, the “main” IP addresses linked to the attack were found to be Russian. It should be noted that it is possible to fake an IP address.

“As with any DDoS attack, there are lots of IP addresses, but the main ones are Russian, though that in itself does not prove anything,” he wrote. “We are still investigating.”

A DoS attack makes sites completely unavailable to their intended users. Many noted that Newsweek’s website was down last night, initially assuming that it was due to high traffic on the Cuba piece. But Eichenwald tweeted Friday morning that the actual issue was an attack on the magazine’s website:

News: The reason ppl couldnt read #TrumpInCuba piece late yesterday is that hackers launched a major attack on Newsweek after it was posted. — Kurt Eichenwald (@kurteichenwald) September 30, 2016

Denial-of-service attacks may be considered a federal crime under the Computer Fraud and Abuse Act.

The story has been updated.