[podperson]

Only someone who believes there are viruses for the Mac are going to fall for this scam, since it's "free antivirus software".

From TFA:

EB: So customers who get hit by this are installing it and giving their admin password?

AC: Yes.

[pygy_]

There are a lot of programs that require the admin password in order to be installed, for them to be installed system-wide... Usually, a single user install would be enough, but they don't provide the option (or I couldn't find it).

As a consequence, users are trained to give their password to random apps, and they end up not paying attention anymore to which app they give it to.