  Thermal infrared detection systems play an important role in many areas such
as night security, autonomous driving, and body temperature detection. They
have the unique advantages of passive imaging, temperature sensitivity and
penetration. But the security of these systems themselves has not been fully
explored, which poses risks in applying these systems. We propose a physical
attack method with small bulbs on a board against the state of-the-art
pedestrian detectors. Our goal is to make infrared pedestrian detectors unable
to detect real-world pedestrians. Towards this goal, we first showed that it is
possible to use two kinds of patches to attack the infrared pedestrian detector
based on YOLOv3. The average precision (AP) dropped by 64.12% in the digital
world, while a blank board with the same size caused the AP to drop by 29.69%
only. After that, we designed and manufactured a physical board and
successfully attacked YOLOv3 in the real world. In recorded videos, the
physical board caused AP of the target detector to drop by 34.48%, while a
blank board with the same size caused the AP to drop by 14.91% only. With the
ensemble attack techniques, the designed physical board had good
transferability to unseen detectors. We also proposed the first physical
multispectral (infrared and visible) attack. By using a combination method, we
successfully hide from the visible light and infrared object detection systems
at the same time.
