When Facebook acquired popular messaging service WhatsApp for an eye-popping $19 billion, other app makers took notice. And, fearful of missing out on a maturing market for “social” apps, some of those companies are trying their hand at what Silicon Valley types call “growth hacking” — or what the average person would call text message spam. Those are the observations of Cathal McDaid of AdaptiveMobile, a network security firm that has produced a report naming some of the worst offenders for growth-hacking.