-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
textField.text = [textField.text stringByReplacingCharactersInRange:range withString:string];

NSString *pass = password;
pass = [pass stringByReplacingCharactersInRange:range withString:string];

[password release];
password = nil;

password = [[NSString stringWithString:pass] retain];

[self hideTextInTextFieldExceptOne:string];

[self performSelector:@selector(hideTextInTextField) withObject:self afterDelay:1.0];

return NO;
}

- (void)hideTextInTextFieldExceptOne:(NSString *)string
{
int lenght = [passwordTextField.text length];

for (int i = 0; i < lenght-1; i++)
{
    NSRange range = NSMakeRange(i, 1);
    passwordTextField.text = [passwordTextField.text stringByReplacingCharactersInRange:range withString:@"*"];
}
}

- (void)hideTextInTextField
{
NSUInteger lenght = [passwordTextField.text length];
passwordTextField.text = @"";

for (int i = 0; i < lenght; i++)
{
    passwordTextField.text = [passwordTextField.text stringByAppendingString:@"*"];
}
}