It's like the difference between a car model and a specific car. A unit type is like ferrari for example while a unit can be your car. That's why, when you create units, it asks you for a unit type. If you wanted to create a car, you would have to tell the manufacturer what car model you want.
A unit type is the stuff that exists in the data editor. A unit is a unit that is on the map and playing. It might have lost some health, it has a position and rotation etc.
The Unit variable stores a specific unit that is in the game, so it can store your firebat as an example.
The Unit Type variable refers to a generic unit type, say a marine or firebat. It is not a particular unit in the game but rather a type of unit.
So when you create a unit, you need to specify the type of unit you want created, so it takes the a Unit Type . The action then creates a specific unit which you reference with Unit variable
Finally finding about some of the bots that are flooding the users online - bytespider apparently is a huge offender here - ignores robots.txt and comes in from a ton of different IPs
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.