I found out what happened. Your tip helped me to troubleshoot. Someone offered me an item called an iPhone which I accepted. But I didn't activate it. It appears I must have activated it unknowingly. Yet the item was not highlighted in the inventory. It's annoying I could not deactivate it, but the activation stopped on its own some minutes later. From now on I won't accept any more items from someone I don't know, or rather, I'll test it out first someplace where I'm alone.