The aim of this study was to investigate Internet use habits and problematic Internet use (PIU) in Turkish adolescents. Participants were 3,975 undergraduate students, 7.6% of whom used the Internet for more than 12 hours weekly. The Online Cognition Scale (OCS) was used. The most common purpose for using the Internet was playing games, followed by general information search. Female users mostly preferred searching for general information; male users preferred playing games (p < 0.001, gamma = 995.205). The most preferred type of game was violent games. While preference for strategy and fantasy role-play (FRP) games increased with age, preference for other games decreased (p < 0.0001, gamma = 283.767). Participants who used the Internet mostly for general information searches and school-related searches had lower OCS scores (p < 0.0001). The highest OCS scores were related to violent games, followed by FRP, strategy, and sports and motor racing games. Computers and the Internet are useful, important inventions, but like other inventions, if used improperly, they may be harmful. Risk of harm raises concerns about who should use the Internet and computers, and where, when, and why the Internet and computers should be used.