Blitzers are a type of player use most or all of there units to take provinces with little or no protection. How they get the information is either from spies or from other countries, possibly even from one you share your map with (traitors).
What to do:
Set up counter espionage, if you get no results, change all shared maps to right of way, leave coalitions if you have to. Let the enemy blitz through you, then sneak troops past the front lines, set many troops in the way of the blitz, when they get to your troops, they will either fall back or get weakened. After that, pounce on the provinces behind the blitz troops, bombard the them, and send troops to finish them, this leaves the rest of the enemy largely unprotected, and you can easily take them.
What to do:
Set up counter espionage, if you get no results, change all shared maps to right of way, leave coalitions if you have to. Let the enemy blitz through you, then sneak troops past the front lines, set many troops in the way of the blitz, when they get to your troops, they will either fall back or get weakened. After that, pounce on the provinces behind the blitz troops, bombard the them, and send troops to finish them, this leaves the rest of the enemy largely unprotected, and you can easily take them.