Update:
The airline, Ryanair, said that a note was passed to cabin crew saying a bomb was on board the aircraft and authorities said all the passengers had left the plane.
http://msnbc.msn.com/id/12285425/
Flight Diversion to Glasgow Prestwick - FR25 Paris Beauvais to Dublin
Flight FR25 from Paris Beauvais to Dublin (today 12th April) was diverted to Glasgow Prestwick on the instruction of the UK Department for Transport, where it landed safely at 14:22. A note was passed to the cabin crew onboard claiming that there was a bomb onboard the aircraft. The Captain immediately reported this to the UK ATC and was instructed to divert to Glasgow Prestwick Airport.
All passengers together with Ryanair are co-operating fully with the police and local safety authorities. The aircraft will now be subject to a detailed search, following which we expect it will be cleared to travel onwards to Dublin.
Ryanair apologises sincerely for any inconvenience caused to these passengers, however the safety of our passengers and aircraft will always be our number one priority. Further updates will be posted on www.ryanair.com as they come to hand.
http://www.ryanair.com/site/EN/notices.php?notice=060412-div-EN