opportunistic

Taking immediate advantage, often unethically, of any circumstance of possible benefit.

Taking immediate advantage, often unethically, of any circumstance of possible benefit; practising opportunism.

Causing disease only when the immune system of the host has been weakened, or other damage to the host provides special opportunity for invasion; -- of microorganisms or infectious diseases.

Taking advantage of situations that arise.

Said of people who will take advantage of situations to advance their own interests, without regard for principles.