Factual error: When Mark types email addresses in to tell people about facemash, he writes to several people @harvard.edu. At the time the movie takes place, undergraduate email addresses were all of the form username@fas.harvard.edu. Furthermore, the network brought down by facemash would have been referred to as the FAS network. (FAS stands for Faculty of Arts and Sciences; the eponymous network covered all buildings within the College and Graduate School of Arts and Sciences.).
Factual error: In the scene of King George V's 1934 Christmas Broadcast from Sandringham, there are factual errors. The B.B.C. Engineers are shown operating Outside Broadcast equipment in a room adjacent to the King - but the equipment (BBC Type OBA/8) didn't even come into service until 1938. It should have been type OB/7 in large mahogany cases. Also, the ornate Royal microphone cases were the wrong ones. These were the later (c1937) type first used by King Edward VIII in his Broadcast in 1936.
Factual error: The construction of Hadrian's Wall as shown at the end of the film is not historically accurate. A wooden wall was constructed first with a deep ditch on either side. One of the ditches should be visible as the characters approach the wall but it is not. The stone wall shown being constructed was not added until later and then it was constructed in sections. It did not become a continuous stone wall until some years later. In addition, the stone wall shown is not wide enough. Hadrian's Wall is around 2 meters wide at the top and even today you can comfortably walk on top of it.
Factual error: Rita says that George was a gunner in the RAF during the war. The photograph of him in uniform in his and Connie's house shows him wearing a (double wing) pilot's brevet instead of the single wing of an air gunner.
Factual error: The attack on the OPEC meeting in Vienna takes place on December 21. Yet, when Carlos' team exits the tram, the trees are full with green summer leaves and the sun shines as it would on a high summer day.
Factual error: When Secretariat crosses the finish line, that finish line pole is not from Belmont, that finish line pole is from Keeneland.