Mr.Smith is a lead incident responder of a small financial enterprise, which has a few branches in Australia. Recently, the company suffered a massive attack, losing$5M through an inter-banking system After an in-depth investigation, it was found that the incident occurred because the attackers penetrated the network through a minor vulnerability 6 months ago and maintained access without being detected by any user. They then tried to delete user fingerprints and performed a lateral movement to the computer of a person with privileges in the inter-banking system. The attackers finally gained access and performed fraudulent transactions.
In the above scenario, which of the following most accurately describes the type of attack?