Where they come from?
I googled out that behind this stand 2 companies - AirPush and SlingLabs, providing developers ability to push messages to notification area.
Investigating each application before installation simply takes too much time and the beauty of Android is its versatility thanks to wide spectrum of applications. Users want to try and use many applications.
Now what to do. Solution for advanced users with rooted devices is bit tricky and it also provides more options. But I want to find easy way for common users.
Solution is relatively easy:
For AirPush visit optout page where you can download simple application which reads device identifications nombers (IMEI...) and send them to system to remove your phone from their database. Or in Google Play is another application called "AirPush Detector"
For SlingLabs has optout page too. But currently not working. I hope they will fix it soon.