Cybercriminals may set up fake Wi-fi networks. Connecting to these fake networks allows them to steal your data (e.g. your passwords). Hackers can also redirect you to fake websites in order to install malware on your computer.
Sometimes, they also use a technique called Wi-fi sniffing. The cybercriminal sets up his laptop close to a Wi-fi hotspot. Using software and a particular type of Wi-fi adapter, he is able to capture all the information passing through the hotspot. He stores them on his hard drive and later searches the data for the most interesting information, such as passwords or account numbers.