From ZDNet.com:
Your pricey smartphone can be hit by a host of security threats, from phishing to malware to spyware. All it takes is one successful attack to clobber your phone, compromise your data, and even steal your identity. So, how do you protect yourself?
Spearphishing attacks can target your phone to install malware, while zero-click exploits can infect your device without any interaction on your part. The NSA’s advice? Power your phone off and then back on at least once a week. This simple action can make it more difficult for hackers to steal information from your phone, though the agency cautions that this will not always prevent an attack.