The BBC quotes a recent computer science PhD graduate at TU-Berlin, apparently with no work or operations experience, on how spies may have intercepted a German military call.

Eyebrows were raised when it emerged the call happened on the widely-used WebEx platform – but Berlin has insisted the officials used an especially secure, certified version. […] A researcher in cryptography in Berlin, Henning Seidler, believes the most likely theory is that the officer dialled in via his mobile phone and the call was picked up by spies’ antenna who can also “forward” the traffic onto the main, official antenna.

Dial-in is an assertion that is easily tested and proven.

Webex for Government supports end-to-end encrypted meetings in Webex App and Webex Meetings.