We are using Google Pub/Sub in the Google Cloud Platform.
There are many anonymous subscriptions listening to our topics. We don't know how and why they have been created.
Is there a way to find out who (e.g. which program, which host, etc.) has created a subscription?
You can look at the activity log for the project to get information about the creation of subscriptions. Under "Resource type" under "Filter," you can choose "Cloud Pub/Sub Subscription":
This will bring up a list of all subscription activity. You can select "Cloud Pub/Sub Topic" to see all topic activity.