It’s a Trojan horse. No different. . . Taking advantage of outdated software and already closed vulnerabilities on the latest two versions of OSX from at least TWO YEARS ago. It IS no different from MacDefender.
And right, it is no virus, technically. In fact, classical viruses are a thing of the past; it is all trojans, nowadays. Calling it “social engineering,” however, is misleading since the malware gets installed even if you don’t cooperate. (The difference is that if you say “yes,” it gets installed system-wide. If not, it will still run under the user account.)