Call from unknown ext... Someone sneak in???

I am a kind of beginner of PBXES having SOHO account.

Sometime I have calls from unknown extension number, which I don't register.
Actually I get it right now and this time I answered it, but no sound and hung in 10 seconds or so.

What is it? ...someone sneak in??
Are there ways of protection??

RE: Call from unknown ext... Someone sneak in???

Hi there!

There may be sip calls to <yourusername>@pbxes.org.

Have you created a inbound route for no numbers?
Usually this '\' route allows unknow traffic.

To prevent, delete the empty route and create a route for every trunk.

Marc