Curses as a result of the direct attack of the enemy
Enter your quote heNumbers 22:1-6 NIV Then the Israelites traveled to the plains of Moab and camped along the Jordan across from Jericho.  Now Balak son of Zippor saw all that Israel had done to the Amorites,  and Moab was terrified because there were so many people. Indeed, Moab was filled with dread because of the Israelites.  The Moabites said to the elders of Midian, "This horde is going to lick up everything around us, as an ox licks up the grass of the field." So Balak son of Zippor, who was king of Moab at that time,  sent messengers to summon Balaam son of Beor, who was at Pethor, near the Euphrates River, in his native land. Balak said: "A people has come out of Egypt; they cover the face of the land and have settled next to me.  Now come and put a curse on these people, because they are too powerful for me. Perhaps then I will be able to defeat them and drive them out of the land. For I know that whoever you bless is blessed, and whoever you curse is cursed."
Deuteronomy 27:15 is a curse against idolatry and is one of the main ways we open our lives to attack by the enemy. Idolatry extends beyond the worship of images and false gods. Idolatry is a matter of the heart - pride, self-centeredness, greed, gluttony, a love for possessions, and ultimately rebellion against God are all forms of idolatry_4. Trusting in anything other than the Lord is a form of idolatry.
Deuteronomy 27:15 NIV
"Cursed is anyone who makes an idol—a thing detestable to the LORD, the work of skilled hands—and sets it up in secret." Then all the people shall say, "Amen!"
Jeremiah 17:5-6 speaks of the man whose heart turns away from the Lord and trusts in his own strength. This is a combination of pride, self-centeredness, and rebellion. All are manifestations of idolatry.
Jeremiah 17:5-6 NIV
This is what the LORD says: "Cursed is the one who trusts in man, who draws strength from mere flesh and whose heart turns away from the LORD.  That person will be like a bush in the wastelands; they will not see prosperity when it comes. They will dwell in the parched places of the desert, in a salt land where no one lives.
In his letter to the Galatians Paul is talking about the same thing as Jeremiah, reliance on the flesh, reliance on your own strength. Can a spirit filled Christian be affected by witchcraft? Paul attributes he Galatians reliance on their own flesh to witchcraft in verse 1.
Galatians 3:1-6 NIV
You foolish Galatians! Who has bewitched you? Before your very eyes Jesus Christ was clearly portrayed as crucified.  I would like to learn just one thing from you: Did you receive the Spirit by the works of the law, or by believing what you heard?  Are you so foolish? After beginning by means of the Spirit, are you now trying to finish by means of the flesh?  Have you experienced so much in vain—if it really was in vain?  So again I ask, does God give you his Spirit and work miracles among you by the works of the law, or by your believing what you heard?  So also Abraham "believed God, and it was credited to him as righteousness."
Results of a curse
In his CD series "Curses: Cause and Cure" Derek Prince summarizes six conditions in a family or a persons life that seem to point to generational curses. Mental and emotional breakdown - not only an individual but in families, repeated or chronic medical problems where there is no clear medical diagnosis, repeated miscarriage or related female problems, breakdown of marriage and family alienation, financial insufficiency especially where the income appears to be sufficient, and being unusually accident prone. This list is not by any means a full list. But these conditions seem to be evidence of a generational curse on a family or an individual. These conditions can happen to anyone and not be the result of a curse. However, the more of them there are in a family the stronger the indications that a generational curse may be the cause. When I look at my family and in my own life I see many of these conditions. I don't have a great deal of detail. However, this study is personal for me and my family.
I have very few living relatives that can provide family history. I have not confirmed but have been told an ancestor was involved in witchcraft, there is at least one ancestor who spent time in jail as a result of being part of a criminal organization. Many of these ancestors lived in various parts of Europe and I have little access to family history, in many cases I do not know the actual family names. But I am confident that God knows my family history and will lead me in breaking these curses.