Andrada Fiscutean, writing for BleepingComputer: When cyber spies known as NetTraveler were busy snooping on hundreds of government and military victims in 40 countries a few years ago, little did they know that another hacking group was probably watching them. During their investigation of NetTraveler, Kaspersky Lab researchers discovered an unusual backdoor that could have helped another attacker access one of their main servers, and then use the group's infrastructure or steal data. In the past five years, cybersecurity experts have encountered several cases in which espionage groups likely pilfered one another's spoils, being interested in getting both data and hacking tools. Kaspersky Researchers Costin Raiu and Juan Andres Guerrero-Saade talked about such incidents on Wednesday during the Virus Bulletin 2017 Conference in Madrid, Spain. Government hackers sometimes "obtain data by stealing it from someone else, who took it in the first place from the victims," Raiu told Bleeping Computer in an email interview before the conference. He and Guerrero-Saade believe that citizens' personal data could fall into the hands of a foreign intelligence agency that's better equipped than the domestic one. The experts based their presentation on so far unpublished research that shows how spies walk off with other spies' data and tools, gaining valuable insight into a foreign service's intelligence collection methods, recruitment tactics, procedural guidelines, and the targets operatives have to monitor.