Lookout Security on Android has been updated today, and it fixes a minor issue pertaining to Google Play. The update reports that an accidental Google Play setting was changed that doubled the size of the application. Lookout apologies for the incident and the app should now be under 6 MB.
The update should be automatic, but if you disabled auto updating then you should have gotten a alert in your notifications. If not, just navigate to the Look out app listing on the Play Store, select it and then click update.