The culprit was found rather quickly. It proved to be inept programmer from Valve, which is placed in the script the following code:
rm -rf "$STEAMROOT/"*
Originally this line was to clear all the contents of a directory with files in Steam, but in some cases the variable $STEAMROOT ran the command to delete all files that can be removed from the user name. Usually, it's the contents of /home:
rm -rf /*
It was found that the error occurred in cases when the user has renamed the directory Steam, or ran Steam with the debug option STEAM_DEBUG=1.
Topic about the problem has already collected more than 200 comments. One citizen of the number of victims unlucky especially before starting Steam he mounted external hard drive 3 TB. All that was acquired by overwork, all died.