WordNet sense 1 (not safe from attack):

insecure

WordNet sense 2 (susceptible to attack):

vulnerable

WordNet sense 3 (not secure; beset with difficulties):

precarious, shaky

WordNet sense 4 (dangerously unstable and unpredictable):

treacherous, unreliable

WordNet sense 5 (fraught with danger):

perilous

WordNet sense 6 (involving risk or danger):

hazardous, risky

WordNet sense 7 (involving or causing danger or risk; liable to hurt or harm):

dangerous