There are a lot of security apps for Android that go a little ways into overkill territory. Whether you're talking about superfluous task managers or "virus scanners" that may provide some minimal protection while generating more fear than is warranted, Android has a persistent problem with companies applying a Windows-era mentality on a completely different OS. Secunia PSI, however, takes the cake for being one of the least effective apps on the Play Store.
Here's how it works: Secunia scans your apps for possible vulnerabilities. Not actual infections, mind you. It just checks to see if the currently installed versions of your application match any known security holes.