Also, some things are commonly recommended to do someone could have the patent to. There was a virtual world I was into a lot in the past and would follow the news on it, and some company was suing them and like 4 or 5 other companies for password hashing. So a method for retrieving a user's account and hashing their password comparing to a stored password hash... Can't find much on it though as was probably about 10 years ago.
Sounds like even patents on implementing two factors or blocking common/weak passwords... Even password resets through email...
Seems like you are likely to step on someone's patent without even reading it or just importing some open source code... unknowingly too. I guess not a huge risk until you are big enough where they'd get a good stream of income from licensing or you fight them off. Like Cloudflare had to deal with a patent troll. Some of these patents are so vague and I noticed some patent trolls use patents that are expiring in a few years since they get traded around. Then some company I heard sued a few companies before their patent expired by only a day or two since I guess even though the patent is expired they couldn't sue new projects using it, but existing stuff filed before it expired in court can still be litigated I guess. Well I guess not suing for current use then, but more the prior use of it infringing over a certain number of years might be another way to put it?
I know some companies tell employees to not read patents, but even if you don't read them might end up getting a patent owner who thinks their patent covers your functions to go after you. I think even someone has a patent on shopping sites where you can select from multiple colors for a shirt or phone, storage options, etc.
Maybe you start a company, get a patent to use to try to protect yourself but not actively going after companies. Then maybe your company isn't doing so well so the investors want you to sell off assets. So maybe a patent troll or shell company buys it up when you never planned on using the patent in that way.
Plus big companies like patents as it's like insurance, I guess there's the nuclear option. So if Apple sued Google over a feature of Android, Google could take a closer look at Apple Maps and say it infringes. So a large patent portfolio could discourage others from suing you. Not sure if that works in all industries but Google and Apple is a good example since a lot of overlapping stuff. I guess Microsoft could also be a good example, if they wanted to sue Google over Google Docs being similar to Microsoft Office maybe over a certain feature they believe they have a patent to then Google could turn around and say Bing infringes on something possibly. Then I think some tech companies rather sue OEMs like HTC and Samsung maybe instead of directly going after each other.