What kind of incomprehensible incoming calls to a soft phone?

Question

SIP

Good afternoon!
The office has VPN and IP-telephony, users can connect via VPN and make calls through ip-phones or soft-phones.
Yesterday I installed MicroSIP on my home PC, set up a VPN, a calling account, everything works.
Moreover, if the VPN is disabled, the SIP server is naturally not available.
This evening, strange incoming calls to my home PC started, but the VPN is disabled, so the account is also offline.
Incoming is displayed like this:

[email protected]<мой_ip>
Кому: [email protected]<мой_ip>
User-Agent: sipcli/v1.8

What are these calls and where do they even call from?
It turns out that you can just call any static IP?

Answer 1

A similar question was raised here icepartners.ru/forum/nastroiyka-3cx/4238-hackery-do...
And here is your number (without the 900 prefix) www.networksystemssolutions.ca/voipblocklist.php
Very similar to viral activity on the network.

Answer 2

It may be that the soft background listens on port 5060 and pretends to be a server. In this case, all incoming via the UDP protocol fall on it.
As an example, a soft background from Yate ( yateclient.yate.ro/). At startup, after some time, incomprehensible calls began. At the same time, I could not start the server on port 5060 (UDP) until I turned off the soft background.
Firewall saves.