What code to hackers use to break into systems?
There are a lot of different programming languages out there and they all have different pros and cons. Injecting java into a system that runs C# isn't going to be very effective as the systems wont know what java code is. Generally speaking though, compiled languages like c# and java dont work very well for hacking because the code wont work unless it has been compiled with the main project. Most hackers will use a scripting language. Something that can be excuted on the fly.
There are two main areas of scripting code that can be used. Languages like Python are very popular because they are powerful, easy to write code for and are used across the internet for so many different things. Getting a python script to execite is possible. PHP is similar. Since a large portion of websites on the internet are using php through the Wordpress CMS, a huge amount of common hacks are going to be written in php. They will use vulnerabilities in public plugins and then take advantage of a web master who may not have locked the system down well enough.
The furious typing you see in movies is generally garbage. If someone gains access to a system, they will likely be using something called a command shell. Windows and linux are the most popular operating systems. Large back end systems will more than likely have linux command line which allows people to use a language known as bash to perform hugely powerful commands once they have super user access. Most of these do not require incredible amounts of typing. Most of the time these commands are fairly short.