I haven't/hadn't checked Skype until now

[EngLearner]

Suppose John hasn't checked Skype for a while. He opens it on his mobile phone and sees a message from his retired employee. He then turns to Bob, who's sitting next to him, and says the following:

I haven't/hadn't checked Skype until now. When I opened it, I was surprised to see there a message from my retired employee.

Which would you use in this case: the present perfect or the past perfect?

 

[teechar]

When I opened it,

Therefore, use "hadn't".