There are a number of online stock brokers but choosing the one who is best for you is a matter of ensuring that your assets and transactions would stay safe from prying eyes. Whenever you compare online stock brokers, you must start by going through the privacy policy of the broker.
The privacy policy provides you the conditions in which your data can be shared with third parties. If the online stock broker is safe, he would only share your data with appropriate law enforcement authorities and that too under proper subpoenas.