An anonymous reader writes: A new study shows that 53 percent of people believe it's legal to install a program on a family member's phone to snoop on their activity. The survey of more than 2,000 people in the US and UK by software comparison service Comparitech.com also finds 57 percent would consider spying on their children's phone conversations and messages. [...] It is generally illegal to install an app on another person's phone without their knowledge. Though this does depend on the circumstances. "It's a legal grey area, in that the laws haven't been truly tested in this arena as of yet since the technology is relatively new, so as relevant cases move through the legal system they'll be decided on a case by case basis," says Josh King, a legal expert in privacy laws and the chief legal officer of Avvo, an online legal marketplace in the US. "Intentional infliction of emotional distress, fraud claims -- all could be implicated, depending on the circumstances. It's also possible that the Computer Fraud and Abuse Act could be used to prosecute someone who installs this type of app on someone else's phone."