Malicious QR codes can be used to hack your laptop or mobile phone. This article from Talos explains how to recognize the threat, and how to avoid it. An interesting item of information is how malicious QR codes can be hidden in innocent-looking images.
Cisco Talos Blog · Malicious QR Codes: How big of a problem is it, really?QR codes are disproportionately effective at bypassing most anti-spam filters. Talos discovered two effective methods for defanging malicious QR codes, a necessary step to make them safe for consumption.