What image does the word 'hacker' conjure up for you? Is it the widely shared picture of an enigmatic hooded man snatching IDs from a spooky basement? The reality is that hacking, like technology, has developed into a hugely terrifying but also highly fascinating topic that continues to change. 

Yet how did hackers start? A handful of MIT students in the Tech Model Railroad Club explored the limits of their model train sets in 1959, and this is where it all started. For the purpose of altering the trains' operations as well as managing the lanes and switches, the club members broke into the sophisticated system that manages the trains.

Today, gaining unauthorised access to a system or device is referred to as hacking. Hackers utilise a variety of methods to get access, including technical ones like viruses or malware and social engineering, which uses psychological ploys to persuade the target to open an attachment or give the hacker access to personal information. Let's examine more closely the technological and social engineering strategies that hackers utilised to carry out these five significant attacks.

First Citibank

In order to steal $10 million from Citibank's phone and computer systems in 1994, Vladimir Levin masterminded the first significant financial robbery The breach happened at a time when many banks were converting to digital systems to cut costs and increase client accessibility. 

The result was a shift toward more computerised services and away from physical branches with tellers. One of these banks, Citibank in New York, was making the changeover to the new cash management system, which permitted electronic money transfers to other banks anywhere in the world. 

Customers' account credentials, such as passwords and account numbers, were stolen by Levin and his small team of hackers in St. Petersburg, Russia, when they provided their information to Citibank staff over the phone. 

Using the credentials, Levin transferred the money electronically to a number of anonymous accounts located all around the world. All but $400,000 of the $10 million was recovered after Levin was apprehended and given a three-year jail sentence.

A virus called Melissa

As the virus with the highest dissemination rate in 1999, an email also served as a cautionary tale about the value of internet security. Targeting Microsoft Word and Outlook-based systems, the Melissa virus was a mass-mailing virus. 

The creator of the Melissa Virus, David Lee Smith, uses social engineering techniques to deliver the virus through email attachment along with a List.Doc document that purported to be a list of passwords for various websites that needed membership. 

The document really contained a Visual Basic Script that, when accessed by users, would disable a number of security features in Microsoft Word. The virus distributed itself to the first 50 contacts in the user's address book if the user used the Microsoft Outlook email software. Due to this, the virus was able to shut down important corporate mail systems. 

Despite the fact that no important data was taken or released, it is claimed to have affected 20% of computers worldwide at the time, costing over $80 million in damages and affecting multiple businesses for several days as they worked to remove the virus from their systems. Smith received a 20-month federal jail term and a $5,000 fine.

The Playstation Network from Sony

Targeted distributed denial-of-service (DDoS) attacks utilise hundreds or thousands of bots to seize control of a system and prevent service from being delivered. In 2011, one such assault targeted Sony's Playstation Network. 

Around 77 million users with accounts on the Playstation Network System have had their personal information, including names and addresses, taken. A loss of over $171 million was sustained as a result of the attack, which prompted the network to go dark for more than 20 days, shutting off players. The attacks were carried out by Anonymous, a well-known hacker collective.

Yahoo!

Yahoo may be the worst offender when it comes to being a constant target of data theft hackers. Three billion Yahoo accounts were hacked in 2013, including names, security questions, passwords, and contact information. 

And to make matters worse, another 500 million accounts were compromised during the same incident in 2014. The biggest hack in the history of the internet was carried out on Yahoo. 

Recently, it was discovered that the attack was carried out by a gang of Russian hackers. By sending spear-phishing emails to Yahoo workers and tricking them into clicking on a link, they were able to access Yahoo's database and steal records and user information.