Hacking is a cybercrime that aims to gain unauthorized access to computer systems, obtain sensitive information, or disrupt operations. Hackers use various techniques to hack into systems, including posting emails with viruses and malware, social networking pages, inserting malicious packets, hacking ads, and probing for weaknesses. They also employ password cracking techniques such as dictionary attack, phishing, and malware to gain access to systems. Hacking is considered illegal when done without authorization or for personal gain, and can lead to serious consequences including financial loss, reputational damage, and even criminal charges.