Users routinely type sensitive data such as passwords, credit card numbers, and even SSN into their mobile phone apps and browsers. Rich functionality combined with weak security mechanisms makes protecting users’ data a challenging. In this talk, I will present a few case studies of applying information flow security to protecting users’ data in Android, the Chromium browser, and the IFTTT framework. For these systems, we show that dynamic coarse-grained taint tracking, even though it allows implicit flows, can be retrofitted into existing systems to defend users’ data from common attacks. I will explain the challenges in striking a balance between preserving key functionality of legacy systems and ensuring formally provable security guarantees and discuss how different modeling techniques affect noninterference proofs.