The focus of malware has changed over time. Originally, there were “free” screen savers and “free” background photography that carried minor reporting functions for advertisers. Then came the background information gatherers that would collect and report to the cloud on anything the computer had done or seen. Later yet came Keyloggers that would capture every keystroke and report that to hidden servers out on the internet. Then came the scams; programs that stated they would remove any of the prior but actually brought in more malware and then held you hostage for anywhere from $20-$800 dollars to get all the crap removed from your system. Recently there have been viruses and malware that encrypt data on your computer and hold you hostage; offering to give you your data back if you pay a ransom. When combined with hacking efforts that add porn to your computer and then open it up as a server any of these become more than just annoying. Oh yeah, I left out the harvesters; malware that harvests all of your mailing lists and then sets your machine up to spam disgusting material out to the mailing lists it has harvested.
Somewhere in the middle of this were corporate supported advertising campaigns where large sales interests pushed seemingly safe and free software out to get research software onto millions of computers to collect information for advertisers without the knowledge of the computer owners (yes, the fine print in the disclosure document did, in most cases, refer to the additional activities of the software being offered; but, the average user had no chance of understanding what that meant). Companies like American Express, and Aurora Group were two that I encountered involving themselves in this behavior; but, I am sure others were involved also.
Today, skilled programmers write “kits” that hackers or unscrupulous entrepreneurs can include in some lovely tidbit of an app or useful add on for your electronic device that turn it into malware or into a trojan horse that will invite oodles of malware onto your device. These kits give the rank and file (average skilled) author the kind of apparent skills that only a rare few have developed and make the whole malware industry flow; much to our expense.