Before revision:  Many existing studies show the vulnerabilities of machine learning and deep learning modelsagainst adversarial examples . {\em   However, most existing works currently focus on evasion attack on text data instead of positioning attack , also named backdoor attack .
After revision:  Many existing studies show the vulnerabilities of machine learning and deep learning modelsagainst adversarial examples . {\em i.e., However, most existing works currently focus on evasion attack on text data instead of positioning attack , also named backdoor attack .