This could be a variety of issues.
It might be ringworm which you can read about here
http://www.marvistavet.com/html/body_ringworm.html
Another possibility is this could be from a tick carried disease such as Lyme disease or Rocky Mountain Spotted fever.
Your vet can test for tick carried diseases.
You can read about tick diseases here
http://www.mirage-samoyeds.com/tick.htm
And depending on where you live those red abdominal spots this time of year can be due to black fly bites. These annoying springtime biting insects are called other names in different areas such as gnats, no-see-ums, midges, punkie etc. Their bites leave a red mark on a dog's skin like a drop of blood staining the skin. The marks are most commonly seen on the abdomen or in areas where there is less fur.
Another possibility is mange mite infection. Usually when seen along the abdomen its contagious mange or sarcoptic mange and you can read about this here
http://www.marvistavet.com/html/body_sarcoptic_mange.html

but it might be non contagious or demodectic mange too

http://www.marvistavet.com/html/body_demodectic_mange.html
And if these spots look more like bruising sometimes a problem with blood clotting will show as that along the abdomen. If the dog might have gotten into a toxin or a rodent bait that could be the issue too.
Your best choice may be to have your vet look at the dog and determine just what is going on to figure out just what treatment is needed. You might snap a picture of the spots to show the vet in case they fade before you see your vet.
Hope this helps you!

I think of it as a true sign of spring just not the most favorite one!

They do make fly sprays for dogs or your vet might suggest something that covers heartworm and repels flying bugs too that is a drop on product.

Its not dangerous its likely just the reaction to the bug bites. Much a like a mosquito bite only not itchy. The bugs when they bite may put in a little anticoagulant to help them get the blood out without it clotting and then it 'stains' under the skin like a bruise from that.

I often use a spray on my dogs so the darn things don't ride in on the dogs and bite me!

A pet supply or feed store will likely carry a dog safe spray if you want to use one.