UPDATE: EXCHANGES INFORMED THEY CAN GO BACK ONLINE:

https://community.electroneum.com/t/exchanges-informed-they-can-resume-etn/5110/3

We’ve just asked ETN exchanges to suspend ETN deposits until we analyse and patch exchange wallets. Monero just found a bug and we are checking to see if we have the same bug, or if it was introduced after we forked from Monero. Normal service will resume ASAP.