The Directional Attack on Wireless Localization -or- How to Spoof Your Location with a Tin Can

802.11 localization algorithms provide the ability to accurately position and track wireless clients thereby enabling location-based services and applications. However, we show that these localization techniques are vulnerable to non-cryptographic attacks where an adversary uses a low-cost directional antenna to appear from the localization algorithm's perspective to be in another arbitrary location of their choosing. The attacker's ability to actively influence where they are positioned is a key distinguishing feature of the directional attack relative to prior localization attacks that use transmit power control to introduce localization errors. We implement a representative set of received signal strength-based localization algorithms and evaluate the attack in a real office building environment. To mitigate the attack's effectiveness, we develop and evaluate an attack detection scheme that offers a high detection rate with few false positives.