only found this not-very-good response in english to those "experts": http://www.vvk.ee/valimiste-korraldamine/vvk-uudised/vabarii...
but saying "terribly insecure" is more than wrong. yeah, thare are many procedural things which could be better, but technologically estonian e-voting is secure. only serious threat is propaganda.
They got away with customer data and who-knows-what-else. I'm pretty sure JP Morgan has a bigger cyber-security budged than the whole state of Estonia, many times over. And then check the laundry list of these: http://cybercampaigns.net/
The basic truth is: we still don't quite know how to design digital information systems that can resist attacks from very persistent or nation state level actors. Even if these are air-gaped (as demonstrated by Stuxnet).
and no matter how big is your budget, kidnapping/blackmailing sysadmins is cheaper :P