All routers are vulnerable to hackers from anywhere. All you can do is common sense stuff like:
1. change admin userid/password from the defaults
2. disable remote access (which I believe is the default on the SmartRGs)
3. update firmware as it's issued
Perhaps one benefit of using a SmartRG modem/router is that because it's a relatively obscure brand, hackers are less likely to target it compared to Asus, Netgear, TP-Link, D-Link, etc. But that's no substitute for the above list.
An update came out just recently: SMARTRG 515AC: FIRMWARE UPGRADEI do wonder if there are ever firmware updates for this SmartRG...
veni, vidi, Visa