The FIA technical officials reported the team to the stewards as data downloaded after the race revealed that Alonso had been able to trigger DRS on three occasions when not within one second of another car.
In theory, the system should only be able to operate when a car is following within one second of another as they pass an activation point.
The officials said that a setting error by the team was to blame, but that the advantage gained had been negligible.
"The DRS enabling system was not changed by the team from the pre-race to the race setting," said a stewards' statement.
"The driver therefore incorrectly received 'DRS enabled' messages and reacted to them (when not entitled to) on three occasions.
"As soon as the team became aware of the problem they informed the driver to only use DRS when told to do so by the team.
"Whilst a small sporting advantage (less than one second over the entire race) was gained, the team argued #3 also suffered a disadvantage by being unable to use DRS on every legitimate occasion.
"However, the team is ultimately responsible for ensuring the system conforms to the regulations."
The stewards chose to bestow a €15,000 fine rather than any form of result penalty.
Alonso therefore keeps his fifth place in the Hungaroring race.