Hackers can exceed the entry limits and DDOS a site in seconds. They are using HTTP, SSL, FTP and SQL. Along with intercepting data and using decryption techniques to see it in plain text. I am no expert; but I have knowledge of how it is done and have worked with their RATs (Remote Access Terminals). The zero day virus was a RAT and could wipe binary, the operating system and the boot sectors; with one button click. It had full access similar to TeamViewer, could look through webcams and it had a built in keylogger.
{snip: no advertising and signatures please}