Tech expert Lance Ulanoff -- who's covered this field as Editor at TechRadar -- came on "TMZ Live" Wednesday to discuss the fatal shooting of Loletha Hall ... who was gunned down late last month in Ohio after 81-year-old William Brock mistook her for someone trying to secure a ransom out of him.

Lance tells us this is an extreme case of these types of stories -- which he says happen all the time, but usually don't rise to this level of violence and tragedy.

Unfortunately, here it did, and he says it's a cautionary tale on the dangers of these bad actors.

He explains the basics of what these scammers do and how they hook people ... and more importantly, Lance gives the telltale signs you might be talking to a fraud on the other end -- and how to avert disaster despite what they might be telling you, scary as it may sound.

Lance says the end goal for these evil people is often just money -- but clearly, it can go beyond that and careen into loss of life, as it did in this case.

He said ... "Their goal is to get money, and it's often a coordinated effort. But, here's the thing you have to understand ... they are starting with all of this information that they have about you because we have been dropping this information about our personal lives on social media for almost 20 years now."

BTW, what Lance is telling us here was doubly confirmed by Ashton Bingham and Art Kulik -- both of whom make up Trilogy Media ... with much of their work dedicated to busting these scammers and exposing them in an on-camera setting.

Ashton and Art also say their hearts go out to Loletha and her family -- as this is obviously the worst-case scenario for a scam like this ... which they too say is all too common.