The Java standard requires that implementations of Object.equals(), Comparable.compareTo(), and Comparator.compare() must return a specified value if their parameters are null. Failing to follow this contract may result in unexpected behavior.

Example 1: The following implementation of the equals() method does not compare its parameter with null.

public boolean equals(Object object)
{
   return (toString().equals(object.toString()));
}

Privacy violations occur when:

1. Private user information enters the program.

2. The data is written to an external location, such as the console, file system, or network.
Example 1: The following code contains a logging statement that tracks the records added to a database by storing the contents in a log file.

pass = getPassword();
...
dbmsLog.println(id+":"+pass+":"+type+":"+tstamp);

The code in Example 1 logs a plain text password to the file system. Although many developers trust the file system as a safe storage location for data, it should not be trusted implicitly, particularly when privacy is a concern.

Privacy is one of the biggest concerns in the mobile world for a couple of reasons. One of them is a much higher chance of device loss. The other has to do with inter-process communication between mobile applications. With mobile platforms, applications are downloaded from various sources and are run alongside each other on the same device. The likelihood of running a piece of malware next to a banking application is high, which is why application authors need to be careful about what information they include in messages addressed to other applications running on the device. Sensitive information should never be part of inter-process communication between mobile applications.

Example 2: The following code reads username and password for a given site from an Android WebView store and broadcasts them to all the registered receivers.

...
webview.setWebViewClient(new WebViewClient() {
  public void onReceivedHttpAuthRequest(WebView view,
        HttpAuthHandler handler, String host, String realm) {
    String[] credentials = view.getHttpAuthUsernamePassword(host, realm);
    String username = credentials[0];
    String password = credentials[1];
    Intent i = new Intent();
    i.setAction("SEND_CREDENTIALS");
    i.putExtra("username", username);
    i.putExtra("password", password);
    view.getContext().sendBroadcast(i);
  }
});
...

This example demonstrates several problems. First of all, by default, WebView credentials are stored in plain text and are not hashed. If a user has a rooted device (or uses an emulator), they can read stored passwords for given sites. Second, plain text credentials are broadcast to all the registered receivers, which means that any receiver registered to listen to intents with the SEND_CREDENTIALS action will receive the message. The broadcast is not even protected with a permission to limit the number of recipients, although in this case we do not recommend using permissions as a fix.

Private data can enter a program in a variety of ways:

- Directly from the user in the form of a password or personal information

- Accessed from a database or other data store by the application

- Indirectly from a partner or other third party

Typically, in the context of the mobile environment, this private information includes (along with passwords, SSNs, and other general personal information):

- Location

- Cell phone number

- Serial numbers and device IDs

- Network Operator information

- Voicemail information


Sometimes data that is not labeled as private can have a privacy implication in a different context. For example, student identification numbers are usually not considered private because there is no explicit and publicly-available mapping to an individual student's personal information. However, if a school generates identification numbers based on student social security numbers, then the identification numbers should be considered private.

Security and privacy concerns often seem to compete with each other. From a security perspective, you should record all important operations so that any anomalous activity can later be identified. However, when private data is involved, this practice can create risk.

Although there are many ways in which private data can be handled unsafely, a common risk stems from misplaced trust. Programmers often trust the operating environment in which a program runs, and therefore believe that it is acceptable to store private information on the file system, in the registry, or in other locally-controlled resources. However, even if access to certain resources is restricted, this does not guarantee that the individuals who do have access can be trusted. For example, in 2004, an unscrupulous employee at AOL sold approximately 92 million private customer email addresses to a spammer marketing an offshore gambling web site [1].

In response to such high-profile exploits, the collection and management of private data is becoming increasingly regulated. Depending on its location, the type of business it conducts, and the nature of any private data it handles, an organization may be required to comply with one or more of the following federal and state regulations:

- Safe Harbor Privacy Framework [3]

- Gramm-Leach Bliley Act (GLBA) [4]

- Health Insurance Portability and Accountability Act (HIPAA) [5]

- California SB-1386 [6]

Despite these regulations, privacy violations continue to occur with alarming frequency.