Arturo is the leader of information security professionals of a small financial corporation that has a few branch offices in Africa. The company suffered an attack of USD 10 million through an interbanking system. The CSIRT explained to Arturo that the incident occurred because 6 months ago the hackers came in from the outside through a small vulnerability, then they did a lateral movement to the computer of a person with privileges in the interbanking system. Finally, the hackers got access and did the fraudulent transactions. What is the most accurate name for the kind of attack in this scenario?