ZURICH (Reuters) - Switzerland’s attorney general has halted an investigation into suspected espionage at a Geneva hotel, which was opened a month after talks on Iran’s nuclear plans took place, but Austria said it was investigating possible spying at later talks in Vienna.

There was a lack of evidence about the people behind the spying, the Office of the Attorney (OAG) said. It opened criminal proceedings in May 2015 after malware was discovered on computers in the hotel.

“Investigations revealed that a significant number of computers (servers and clients) at a hotel in Geneva had been infected with a form of malware,” OAG said in a statement on Thursday. “This malware was developed for the purposes of espionage, and is basically used to gather data from the computers infected.”

A source said the malware was discovered on computers at the Hotel President Wilson, where talks on Iran’s nuclear work had taken place a month before, following a tip off from the Swiss intelligence services.

The attorney general’s office said it was suspending proceedings because no evidence regarding the perpetrators’ identities had been obtained.

Austria, however, said prosecutors in Vienna were conducting an investigation in relation to a later round of Iran talks in the Austrian capital that led to a landmark agreement last year under which restrictions were placed on Tehran’s atomic activities in exchange for a lifting of international sanctions.

The Vienna prosecutors’ office was investigating on the suspicion that two crimes were committed - misuse of audio recording and listening devices, and secret intelligence service activity to the detriment of Austria - by persons unknown, the Justice Ministry said in response to an inquiry by Reuters.

It declined to elaborate.