One in five Scots caught the winter vomiting bug last year, 30% more than the average for the last five years.
Exactly 2824 cases of norovirus were confirmed by labs in the first 51 weeks of 2012, according to figures released by Health Protection Scotland (HPS).
But experts believe for every confirmed case, there could be between 239 and 346 unrecorded cases in the community.
Using these figures, that means 977,104 people in Scotland could have been hit by norovirus in the first 51 weeks of 2012.
As the statistics for the last week are not yet available, the number for the whole year could be as much as a million.
Dr John Cowden, a health protection consultant at HPS, explained the reason for such an apparently large number of unrecorded cases.
He said: "Almost everyone affected with norovirus is only mildly ill and will not visit a health professional. If a health professional does see them, they will not necessarily take a specimen. Even if doctors do take a sample, laboratory testing is not 100% sensitive."
Last year's figure shows a 75% increase on the 2011 level although experts stress it was the lowest recorded annual figure since 2005.
Nausea followed by vomiting and diarrhoea are the main symptoms of norovirus. Those who catch the bug are advised to drink plenty of non-alcoholic, non-milky drinks and also take oral rehydration solutions.
Those infected should ensure their hands are clean to prevent the infection from spreading and should not prepare food for others, particularly babies and elderly people.
Chief Medical Officer Sir Harry Burns said: "Norovirus, or the winter vomiting bug, can spread quickly where people are living or working in close proximity. The virus is highly infectious and unpleasant but, fortunately, most people make a full recovery with no complications.
"Rates of norovirus fluctuate from year to year with occasional spikes. The Scottish Government and health boards monitor norovirus outbreaks closely throughout the year, taking every step to minimise its impact on people who use and work in our hospitals.
"There are simple steps that everyone can take to prevent the spread of the virus, including washing your hands properly."
The data for 2011 remains provisional
The data for 2012 only includes the first 51 weeks