Hello Joe!
The aircraft the Swedes used was a Spitfire XIV PR. Sometime after the war Swedes had learned from POWs that the Soviets are constructing rocket stations near the Finland border in Kantalahti (Kandalaksha).
Swedish Air Force sent Lieutenant Ingemar Wängström in civil clothes and over-painted Swedish markings in his Spitfire to photograph these sites.
After analysing the 200 meter long film that Wängström had photographed the Sweden's HQ noticed no rocket stations at the area. Six MiG-15s (3 pairs) had followed the Spitfire but non of them got enough close to shoot.
The overflight was observed by Finnish Border Guard, but Swedish goverment denied any flight over Finland and USSR in 20.12.1949.
Sources:
http://www.pohjolansanomat.fi/teema/viikonvaihde/884166.shtml
http://www.avrosys.nu/aircraft/Spaning/217S31.htm
I have reserched this subject a quite time and I haven't seen an one case when FiAF's aircraft has engaged an "enemy" aircraft. Though there have been many occasions when USSR plane has crashed to Finland's soil (MiG-15 in 1950's and russian cruise missile in 1984). Furthermore FiAF shot down few weather balloons during the cold war.
RB-47E was almost shot down over Finland in 1954 by MiGs when returning from a spyflight.
http://www.rb-29.net/HTML/31HAustinB-47/31harb-47.htm
Martti