Many Android devices of that age and even newer had flaws resulting in the failure to properly validate HTTPS connections as they would accept invalid certificates. As a result, every time I fire up an off the shelf WiFi Pineapple in public and run SSLSplit (not to be confused with Moxies SSLStrip), I get credential after credential, typically starting with e-mail accounts. This is obviously bad because if someone is using an e-mail account on their phone for banking, an attacker could gain access to account recovery.

These are the sorts of transparent attacks you don't notice and which cannot be mitigated with anti-virus or avoiding downloading sketchy apps. The sketchy stuff is already running on the device in the form of the OS and apps you use within it. Note that a large number of these vectors were never publicly disclosed including a vulnerability with Samsung Knox that I reported. When it was in use, the device would accept any cert.