Authorities accused the U.S. of spying on German Chancellor Angela Merkel, pictured at an EU summit in 2014. An investigation was opened Oct. 24, 2015, into fresh allegations against the National Security Agency. AFP/Getty Images

German authorities have opened an investigation into a potential case of U.S. spying led by the National Security Agency (NSA), German magazine Der Spiegel reported Saturday. The case came following accusations in 2013 that U.S. authorities had spied on German Chancellor Angela Merkel by bugging her cell phone.

"We can confirm that there is an inquiry" relating to "malicious software," a spokesperson for the German federal prosecutor told Agence France-Presse.

The inquiry surrounds malicious software called Regin, allegedly produced by the NSA. The software works like a Trojan Horse virus, entering a computer and uploading data to whoever installed it. At least one member of the chancellor's office has been affected by the software.

The fresh allegations came after charges were dropped in June regarding U.S. spying on German authorities. Former CIA employee and whistle-blower Edward Snowden revealed in 2013 the U.S. had been tapping Merkel's phone as well as those of other top ministers. After nearly two years of investigation, the charges were dropped in June for lack of evidence.

Regardless of the results of the investigation that ended in June, German government officials have sought to reinforce the nation's anti-surveillance technology to prevent any future spying, and spokespeople from the government said they were more confident than ever, according to a June statement. “The government has already strengthened its anti-espionage operations since last year,” said Steffen Seibert, a government spokesperson, as reported by the Wall Street Journal in June.

Edward Snowden interviewed by Jane Mayer at the MasterCard stage at SVA Theatre during the New Yorker Festival, Oct. 11, 2014, in New York City. Bryan Bedder/Getty Images for the New Yorker

News of the case came several weeks after Germany opened an investigation into its agency's own rogue spying. German intelligence service Bundesnachrichtendienst allegedly spied on the U.S., France and other allies without the express permission of the German government as recently as 2013, an October report from Der Spiegel said.