A small mob of privacy advocacy groups have called on Facebook CEO Mark Zuckerberg to do more to protect user privacy by giving users more control over the way their personal information is turned over to third parties.

In a letter sent Wednesday, the groups – which included the Center for Democracy and Technology and the Electronic Privacy Information Center – acknowledged that Facebook has gone a long way to fixing the privacy blunders that have brought international condemnation to the social networking site.

“However, we are writing to urge you to continue to demonstrate your commitment to the principle of giving users control over how and with whom they share by taking these additional steps,” they wrote.

They went on to catalog six remaining features that jeopardize user privacy, chief among them an “app gap,” that allows applications to access a user's information even when she has never run the program. That's because an app has access to the data as long as any of that user's friends run it.

“Facebook's latest changes allow users a 'nuclear option' to opt out of applications entirely,” Wednesday's letter acknowledged. “While this is an important setting, it is not adequate for meaningful control. Facebook users should also have the option to choose to share information only with specific applications.”

Other steps include:

* Make “instant personalization” opt-in rather than opt-out by default

* Don't retain data about specific visitors to third-party sites that incorporate social plugins or Facebook's “like” button” unless the user chooses

* Provide users with control over every piece of information they can share, including name, gender, profile picture and networks

* Offer encrypted HTTPS connections for all interactions and

* Provide users with simple tools for exporting their uploaded content and details of their social networks so it's easier for users to leave Facebook for a competing service

The letter comes a few weeks after Facebook touched off a firestorm by loosing user privacy controls and putting them in place without getting explicit permission first.