vipers are technically "venomous", not sure what you have in scandinavia, but in general vipers are dangerous (meaning, if you will not be treated with antivenom in a very short amount of time, usually somewhere bellow 30minutes, but it depends, you will die (painfully)). in some areas/countryes, the corollary to the above is "if you get bitten you will die.", but that's msot likely not the case in scandinavia, considering what sort of social/medical system you have back there. ofcourse, that might just be some snake, not a viper, and be "mostly harmless" (TM of "don't panick" (R) ), really can't tell from the picture.
the best advice would be to check the details for your area, maybe try to identify the species you are dealing with in this particular case, and be careful meanwhile (especially if you also have children playing in that yard and so on), you might find you would rather have her relocated (don't kill her, they are amazing creatures, would be a shame)
nice shot