  Smartphones and tablets have become ubiquitous in our daily lives.
Smartphones, in particular, have become more than personal assistants. These
devices have provided new avenues for consumers to play, work, and socialize
whenever and wherever they want. Smartphones are small in size, so they are
easy to handle and to stow and carry in users' pockets or purses. However,
mobile devices are also susceptible to various problems. One of the greatest
concerns is the possibility of breach in security and privacy if the device is
seized by an outside party. It is possible that threats can come from friends
as well as strangers. Due to the size of smart devices, they can be easily lost
and may expose details of users' private lives. In addition, this might enable
pervasive observation or imitation of one's movements and activities, such as
sending messages to contacts, accessing private communication, shopping with a
credit card, and relaying information about where one has been. This paper
highlights the potential risks that occur when smartphones are stolen or
seized, discusses the concept of continuous authentication, and analyzes
current approaches and mechanisms of behavioral biometrics with respect to
methodology, associated datasets and evaluation approaches.
