A public wireless network or Wi-Fi is a potential paradise for unethical hackers and schemers since these networks are not secured. Use one only if you must, then too whenever you are connected to a public network, refrain from using this connection to make online purchases requiring use of credit cards, viewing your bank statements or making online money transactions from your bank accounts. Even though these accounts are password protected, since the network is not secure, someone with the right tools and knowledge can easily view what you are doing online and also view all the websites that you are visiting and may use this knowledge to extract your important details and may result in identity theft or duping you to monetory losses!
Also, it is equally important that you refrain from giving out your personal information such as name and address, telephone numbers etc. in any way while using free network.