I don't understand this blasphemy against the Holy Spirit. I know it's not hating or cursing God. I know that in Bible we have examples like when Jesus healed a man and the Pharisees claimed that he use devil's power. Still, 2000 years later, people still fear of this sin, and no one claims such thing as the devil's power, so what is the modern concept of this sin?
Blasphemy is knowingly and purposely slandering the Holy Spirit, such as by taking the clear evidence of God working a miracle (done by the Holy Spirit's power) and claiming it was the work of Satan. I've seen people do similar things by claiming the Bible is the work of the devil -- not because of disbelief, but because they did not want to accept what God said. They knew the Bible was from God but purposely said it was from Satan.
When a person gets to that point, there is nothing anyone can do to bring them back to God. God isn't going to offer any other proof and the person isn't going to accept what is given. Thus, the person won't repent -- not because he is unable to repent, but because he stubbornly refuses to change. Without repentance God is unable to offer forgiveness.
Many weak-willed people want to imagine they had blasphemed the Holy Spirit. It is the ultimate expression of victimhood in their mind because they can pretend that God refuses to forgive them. In reality they can't forgive themselves, but they would rather blame God than face reality.
What most people don't realize is that blasphemer doesn't care. He isn't concerned about what God thinks or other people think. He has no worries because he is absolutely certain he is right.