From the article "but they [the companies] can be forced to keep quiet about it in order to avoid exposing active investigations and alert those targeted by the probes."

There are a number of reasons why both the government and the companies would want to keep it secret:

1. Bad reputation for the company.

2. Bad reputation for the government on how much spying they actually are doing.

3. "keep quiet about it in order to avoid exposing active investigations" (this point I would think to be irrelevant in this case however)

The US companies can be forced by the US government to be kept quiet about the data they revealed. However, their subsidiaries are European companies, and therefore must comply to EU law, therefore they shouldn't share the data, and if they do, that's a crime, and if they furthermore keep quiet about it, it's an even bigger crime.

I think they should be punished by law to the fullest extent available. Along with everybody that was responsible and is within the reach of EU law.

Actually, the EU should request extradition of those responsible that reside in the US, even if they didn't break the US law. Fair, isn't it?

> There are a number of reasons why both the government and the companies would want to keep it secret:

Which are much the same reasons why someone who has stolen a TV would want to keep that secret. It doesn't make it an idea worth encouraging.

I'm sure that a secret agreement between EU governments and the US have been reached, as is the case when security is involved.

Quite likely. That'd doesn't make it legal, necessary or even a good idea.