What does "DEL:" mean in the DistinguishedName of an AD Object?
Solution 1:
These are deleted objects. The process happens when an object is deleted so that other domain controllers can be made aware of the deletion. This is documented in great detail on TechNet.
Don't delete these, write your program to not return them as results. Excluding CN=Deleted Objects, DC=Domain, DC=tld from your queries should be enough, as this is where they're all put.