Westchester County on Thursday enacted a law that is designed to limit identity theft by forcing local businesses to install basic security measures for any wireless network that stores customers’ credit card numbers or other financial information. The law also requires that businesses offering Internet access — coffeehouses and hotels, for example — post signs warning that users should have firewalls or other security measures. The law requires each business to install a firewall or change the default SSID, the name that identifies a wireless network, if the personal information stored has not already been encrypted.