Information can be negative

 Jonathan Oppenheim wrote: 

What could negative information possibly mean? In short, after I send you negative information, you will know less. Such strange situations can occur because what it means to know something is very different in the quantum world. In the quantum world, we can know too much, and it is in these situations where one finds negative information. Negative information turns out to be precisely the right amount to cancel the fact that we know too much [1]. 

[1] Source of the quote here