Online venues may be more vulnerable to certain types of fraud, especially collusion between players. However, they have collusion detection abilities that do not exist in brick and mortar casinos. For example, online poker room security employees can look at the hand history of the cards previously played by any player on the site, making patterns of behavior easier to detect than in a casino where colluding players can simply fold their hands without anyone ever knowing the strength of their holding. Online poker rooms also check players' IP addresses in order to prevent players at the same household or at known open proxy servers from playing on the same tables. Digital device fingerprinting also allows poker sites to recognize and block players who create new accounts in attempts to circumvent prior account bans, restrictions and closures.