Georgie Casey, who runs a popular Android app-development blog in Ireland, created a modified (backdoored) version of SwiftKey using a tool called apktool combined with basic knowledge of Java and Android. The end result was a backdoored app called Keylogger SwiftKey APK, which Casey made available from his website (along with explicit warnings that it was to be used by interested parties and only to validate the problem).
"Apktool isn't keylogging software, it's an Android app dissassembler," Casey told El Reg.
"You dissassemble a Swiftkey keyboard, code your keylogger code that sends keylogs to my server, re-assemble with Apktool and now you've a keylogger. You still have to convince people to install it though.""