Roth said he had released the video now because ProtonMail had fixed various flaws he reported back in May via email. However, the Swiss consortium hadn't credited or warned users of his discovery, he claimed, hence his open disclosure of the bugs.
"The reason I posted the video was because they did not communicate the security problems to their users – and did not even notify me when the bugs were patched," Roth told The Register.
"I believe that for a service that is used for 'secure communication' trust is very important – and if they hide vulnerabilities from their users I can not trust them."
The researcher said he had reported five vulnerabilities including a cross-site request forgery bug that apparently allowed an attacker to change victims' email signatures, further opening them to malicious cross-site scripts.
In response, ProtonMail said the problems Roth highlighted had been fixed, and added that they were no longer an issue.
But it does say something about the state of play in the industry when a system designed from the ground up to be secure is defeated by what is a relatively common attack vector. ®
Updated to add
While ProtonMail has fixed the bugs highlighted, the company said it would welcome additional security advice.
"ProtonMail is constantly making security improvements through our beta process and we appreciate all the assistance we have received from the community in helping us make ProtonMail better. The concept of encrypting on the client side is a relatively new one and comes with its own security challenges which we are working diligently to tackle," the outfit said in a statement to El Reg after our story was published.
"The ProtonMail security team has reviewed the video released by Mr Roth and confirmed that this particular security issue is not present on the live version of ProtonMail. Mr Roth's video appears to be using an earlier development release of ProtonMail that was originally released on May 10th, 2014 for public testing. We are supportive of all efforts to improve the security of ProtonMail and security inquiries can always be directed to email@example.com."