  We show that the new hover (floating touch) technology, available in a number
of today's smartphone models, can be abused by any Android application running
with a common SYSTEM_ALERT_WINDOW permission to record all touchscreen input
into other applications. Leveraging this attack, a malicious application
running on the system is therefore able to profile user's behavior, capture
sensitive input such as passwords and PINs as well as record all user's social
interactions. To evaluate our attack we implemented Hoover, a proof-of-concept
malicious application that runs in the system background and records all input
to foreground applications. We evaluated Hoover with 40 users, across two
different Android devices and two input methods, stylus and finger. In the case
of touchscreen input by finger, Hoover estimated the positions of users' clicks
within an error of 100 pixels and keyboard input with an accuracy of 79%.
Hoover captured users' input by stylus even more accurately, estimating users'
clicks within 2 pixels and keyboard input with an accuracy of 98%. We discuss
ways of mitigating this attack and show that this cannot be done by simply
restricting access to permissions or imposing additional cognitive load on the
users since this would significantly constrain the intended use of the hover
technology.
