Wireless local-area networks (WLANs) are increasingly common in public locations such as urban areas, universities, airports or shopping centers. A clear understanding of usage behavior in real hotspots is critical information for those who develop, deploy, and manage WLAN technology as well as those who develop systems and application software for wireless networks. This thesis analyzes user behavior and network performance in public wireless networks in Helsinki, collecting traffic traces over several days at different access points. The analysis covers locations, which provide hotspots connectivity in different social environments including, libraries, museums or cafeterias. The capture process focuses of open access point infrastructures, where the access to the Internet is free and becoming ubiquitous. This enables the study of user behavior in urban environments. The first part of the thesis introduces the research field on a general basis, a literature survey is given to present the current state-of-art. The survey covers technologies and issues in open WLAN networks, relevant terminology and privacy aspects concerning the traffic collection. The performed research and capture methodology is then presented. The focus is on the challenges in wireless monitoring and data collection. The findings and part of the thesis discusses the results from the capture analysis to evaluate the Internet usage in a public wireless LAN environment. As an outcome, the thesis describes how free hotspots provide services to a diverse population that use the WLAN through open access points. In particular, web based applications are the most popular with the clients in this study. The traces show variable web response delay and different connectivity durations for browsing behavior and diversity of user attitudes depending on the location.