Engage Recovery Experts
It is essential to involve an expert at the earliest possible opportunity. The sooner an expert can investigate and respond to the attack, the less damage to your computers and IT network.
An expert IT team can limit the spread of the attack and repair the damage. They can also help to rebuild your system with stronger protection.
They will also be able to tell you whether the attack was an untargeted, mass-produced attack (e.g. something an employee might have picked up by browsing a compromised website) or whether it was a unique targeted attack, which is of greater concern.
Whatever you do, do not delay getting an expert involved.