I have the latest Avast running on a Moto G LTE phone (installed more than a year ago, regularly updated) under Android 5.1.1. Recently I noticed that upon every reboot the phone sends 2 messages to each of my AntiTheft contacts, as well as one SMS to +42072001669 and another to +338420720001669 (fails to be delivered to the latter).
THIS IS SURELY A BUG, as I have not changed or removed the SIM for ages. _The behavior is apparently caused only by shutdowns due to low battery_.
If this matters for troubleshooting: my phone is also protected by a pattern and the SIM is set to unlock with a PIN code.
BTW, the "empty" messages sent to my contacts do not reach them, even though those numbers are operated by the same cellular network and the plain old Samsung phones run no blocking software.