It sounds like the title of a really bad horror movie, but it was a for-real curse that happened in 632BC.
There was at that time in Athens a famous Olympic victor called Cylon. Like many famous people to this day, Cylon assumed that fame in one field guaranteed success in another. He should have consulted with a career advisor, because unfortunately his chosen new life plan was to make himself the Tyrant of Athens.
In his defence, it must be said that Cylon was probably encouraged by his father-in-law, who happened to be the tyrant of a city called Megara, just up the road. Sometimes it can be really tough for a guy to impress the wife's family.
It all went horribly pear-shaped when Cylon gathered together his friends and attempted an armed takeover. He seems to have assumed the common people of Athens would flock to his leadership when they saw what was happening. But when the fighting began, the people of Athens were notable by their absence, and Cylon and his followers had to retreat to the temple of Athena atop the Acropolis. (Not the Parthenon. The Parthenon would not be built for another 200 years.)
Then Cylon managed to escape, leaving his hapless friends trapped inside the temple, to face the consequences of his ambition. By the end of the day, Cylon had set a new record for total leadership FAIL.
Now everyone had a problem. As long as the coup plotters stayed inside the temple, they were safe, because all Greek temples had sanctuary. Anyone who harmed a person under the protection of Athena was looking at some serious trouble. (Cylon's friends were neither the first nor last to rely on temple sanctuary for protection; it was perfectly normal for pursued criminals to make a beeline for the nearest altar.)
Negotiations began between the coup plotters and the archons (city officials). The archons convinced the men to come out, in return for a fair trial. I can't imagine what fair trial the plotters thought would result in them surviving, but presumably they planned to argue it was all Cylon's fault.
There are different stories about what happened next. The most dramatic says the plotters emerged, tied to a rope which they'd fastened at the other end to the cult statue of Athena within the temple, to maintain their connection with the Goddess.
Another version says the archons swore before Athena that the plotters would have sanctuary while the law took its course. Either way, everyone agrees the men were under the protection of the Goddess when they emerged to go to the place of trial, which certainly would have been the adjoining rock of the Areopagus.
Among the archons was a man called Megacles, from the genos (family) Alcmaeonidae (ALC-MAY-ON-ID-AY). When the friends of Cylon were out in the open, the archon Megacles and all the men of his family fell upon them and killed them.
No one cared about the dead plotters, but the men of the Alcmaeonidae had just broken the sacred sanctuary, and that was a big deal. A very big deal.
Megacles claimed (in the rope version) that they'd seen the rope break, meaning Athena had repudiated her protection. But that weak excuse didn't wash.
At once a curse fell upon the family - in Greek, a miasma - and not just upon the men who committed the crime, but upon every member of the family. And not just those living, but every man, woman and child to be born into the family forever after.
This crime was so bad that the Alcmaeonidae were, in fact, eternally cursed.
To expiate the sacrilege, and to avoid a furious Athena from destroying her own city, Megacles and the Alcmaeonidae were expelled from Athens.
Then they dug up the remains of dead members of the family and threw them out too.
That's the way things stayed for 40 years, until Solon the Wise allowed the family to return, because Solon was a weak-kneed, bleeding heart, soft-on-crime wimp. Or so the dissenting Athenians thought as the accursed family walked back in the gates. Nevertheless Athens failed to be destroyed by the Alcmaeonid presence, and things settled down.
Now the Alcmaeonidae were destined to become a driving force behind democracy. Note that the crime for which they'd been cursed was the ruthless slaughter of would-be tyrants.
Eighty years later, a tyrant did manage to take Athens, and the Alcmaeonidae had a very uneasy relationship with him. The family head at the time - another Megacles - married his daughter to the tyrant, which kept the peace for a while, but eventually the Alcmaeonidae were instrumental in removing this tyranny too. Supporting freedom was obviously a family tradition.
Then an Alcmaeonid called Cleisthenes introduced the democratic reforms which led to full democracy 50 years later under Ephialtes. When Ephialtes died, he was replaced by Pericles, who was...you guessed it...an Alcmaeonid on his mother's side.
But it didn't matter how successful the Alcmaeonidae became; whenever a member of the family was put in charge of anything, someone was bound to ask, "But what of the curse?" Even the Spartans raised it when they were dealing with Pericles, 200 years after the crime.
It must be pointed out that the curse on the family was eternal. Which means their descendants living today, of which there must surely be some, are in fact, cursed.