Prevent sensitive information from appearing in the screenshot that is automatically taken when the application transitions from the foreground to the background and vice-versa.

UIViewController+MBSensitiveInformationInScreenshotPrevention.h

//
//  UIViewController+MBSensitiveInformationInScreenshotPrevention.h
//
//  Created by Manuel Binna on 05.05.11.
//  Copyright 2011 Manuel Binna. All rights reserved.
//


@interface UIViewController (MBSensitiveInformationInScreenshotPrevention)

// Hide the root view of the view controller's view hierarchy when the application did enter background or when the application will terminate.
- (void)mb_startPreventingSensitiveInformationFromAppearingInScreenshot;

// Un-hide the root view of the view controller's view hierarchy when the application will enter foreground.
- (void)mb_stopPreventingSensitiveInformationFromAppearingInScreenshot;

@end

UIViewController+MBSensitiveInformationInScreenshotPrevention.m

//
//  UIViewController+MBSensitiveInformationInScreenshotPrevention.m
//
//  Created by Manuel Binna on 05.05.11.
//  Copyright 2011 Manuel Binna. All rights reserved.
//

#import "UIViewController+MBSensitiveInformationInScreenshotPrevention.h"


static NSMutableArray *mb_registeredObservers;

@implementation UIViewController (MBSensitiveInformationInScreenshotPrevention)

- (void)mb_startPreventingSensitiveInformationFromAppearingInScreenshot {
    // Need to store the registered observers to be able to unregister them later.
    if (mb_registeredObservers == nil) {
        mb_registeredObservers = [[NSMutableArray alloc] initWithCapacity:3];
    }
    
    __block __typeof__(self) blockSelf = self;  // Prevent creating a retain cycle.
    id observer = nil;
    
    observer = [[NSNotificationCenter defaultCenter] addObserverForName:UIApplicationDidEnterBackgroundNotification object:nil queue:[NSOperationQueue mainQueue] usingBlock:^(NSNotification *notification) {
        blockSelf.view.hidden = YES;
    }];
    [mb_registeredObservers addObject:observer];
    
    observer = [[NSNotificationCenter defaultCenter] addObserverForName:UIApplicationWillTerminateNotification object:nil queue:[NSOperationQueue mainQueue] usingBlock:^(NSNotification *notification) {
        blockSelf.view.hidden = YES;
    }];
    [mb_registeredObservers addObject:observer];
    
    observer = [[NSNotificationCenter defaultCenter] addObserverForName:UIApplicationWillEnterForegroundNotification object:nil queue:[NSOperationQueue mainQueue] usingBlock:^(NSNotification *notification) {
        blockSelf.view.hidden = NO;
    }];
    [mb_registeredObservers addObject:observer];
}

- (void)mb_stopPreventingSensitiveInformationFromAppearingInScreenshot {
    NSNotificationCenter *defaultCenter = [NSNotificationCenter defaultCenter];
    [mb_registeredObservers enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
        [defaultCenter removeObserver:obj];
    }];
    
    [mb_registeredObservers release];
}

@end