Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
It is extremely forbidden in Islam to see blue films; this is something that there is no doubt about. The Prophet (Sallallahu Alaihi wa Sallam) called looking to what is Haram Zina (fornication), he said: "The eye commits Zina and its Zina is looking (at what is forbidden)." This Hadith is reported by Ahmad and others, narrated by Abu Hurairah.
This is more serious if it happens during Ramadan. A Muslim should spend Ramadan in obedience and repentance from sins, striving to acquire piety.
Therefore, one should be very careful, Allah Said (interpretation of meaning): {Tell the believing men to lower their gaze (from looking at forbidden things), and protect their private parts (from illegal sexual acts, etc.). That is purer for them. Verily, Allâh is All-Aware of what they do.}[24:30].
The Prophet (Sallallahu Alaihi wa Sallam) also said: "Looking (or viewing) is one of the arrows of Satan." Narrated by Al-Tabarani and Al-Hakim who said that this is an authentic Hadith.
A person who watched these bad films must repent truly to Allah and seek forgiveness as Allah forgives those who repent.
Allah knows best.