GCM Topics over-subscribing attack?

[Clarence Ho]

Hi,

I just created an Android application using GCM to receive Topics messages.  Everything works fine but I have some questions on the mechanism.

How secure is the GCM Topics workflow? Since anyone can subscribe to my topics using the sender ID (which is embedded in the APK), seems to me that it is possible to launch a DoS attack by over-subscribing my topics (as there is a 1M limit for each app).

Also, is there any tool to monitor the number of subscriber?  Couldn't find it on Developers Console.  I would like to monitor the status before it reaches the 1M limit.

Thanks.

Regards,

Clarence