system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does everyone hate flash so much? Why is everyone trying to get it blocked everywhere?
gpt
Flash is a system where web designers can do things on a webpage that is not usually possible through html.  It can play video, connect to servers, read and write to the operating system files, and more.

Unfortunately, to achieve all of these features, flash had to give its programs increased access to the operating system.  Flash tried to protect the operating system by creating a 'sandbox' - forced limitations of how the flash programs can use the operating system, but Flash has failed to keep its programs in the sandbox in many, many cases.

So now a programmer could use one of these holes in the sandbox to install viruses, steal data, control the web browser, and other bad activities.  Flash tries to block the holes, but new ones keep popping up.  The public has lost trust in Flash, and now there are efforts to remove it completely from the web to better protect all of us users.

Additionally, advertisers were able to use Flash to to make the web annoying.  Advertisements would make noise, flash, play video, and talk.  Compared to the pages, the flash advertisements were large and could slow down the computer.  So now you are trying to read the news, and right in the middle of the article are 3 monkeys trying to dodge your mouse cursor, a car driving through a box, and bags of money enticing you to click on one. So in addition to the security issues, Flash became synonymous with advertising, attracting even more hatred.