With the advent of the smartphone, companies are trying to get more and more information about their users by giving away applications for free. Web-based services companies are notorious for this.
Recently it was discovered that by installing the Facebook App into your iPhone, your complete iPhone contact list is imported into Facebook’s systems. More on there here.
When installing any application on your devices, it is good practice to evaluate the level of trust you have of the source. Viruses via email are no longer the issue. We must now be away of software whether it be something we install or something a malicious site tries to install when we visit that URL (Malware).