You're right, Rooster. Law enforcement gets very difficult on the Web. But Wat is right, too. Education would help but there's no cure for stupidity.
Sure there's a way to prevent it ... Don't open any attachment, unless you are 100% positive it's safe.
Our IT department had to "scrub" a virus from the hospital computers a few months ago, because somebody was reading their personal email at work and opened an attachment from an advertisement. It took a week to get it out of all the "nooks and crannies" in the network - and we're a small hospital.
Or somebody falls for the "warning" about a virus, when they are browsing online and clicks on the link to "clean" their system.
It's all about education.