FireEye: Free Android apps available from the Google Play Store with over one million downloads have been found using vulnerable cryptographic systems to protect sensitive information they store.
An analysis of the most popular free apps (9.339 apps) available in the official Google Store reveals that about 62% of them, or 5.147, were unable to properly secure confidential information, which could allow an attacker to steal the "protected" data by exploiting various weak points.
Her researchers FireEye (you can read more on the official website) did the tests on samples that met the popularity criteria mentioned above at 22 November 2014.
Experts looked for vulnerabilities in high entropy, encryption algorithms, and encryption codes.
Most of the products found cryptographically unsafe were with cryptographic algorithms. An attacker could use a reverse dictionary to discover the original string without knowing the keys used for encryption.
The cases of low entropy weaknesses discovered by the security company concerned 1.762 applications that used a static key to encrypt the information that could be extracted to reverse the process.
So beware of what you download, or to be even more confident, of what you store on your devices.