Just how exactly identifiable does information have to be before it counts as "personal information"? This is the question the full Federal Court is weighing up as the Privacy Commissioner and Telstra battle it out over the metadata of a former Fairfax journalist.

The three-year old case stems back to June 2013, when then-deputy technology editor for Fairfax Ben Grubb asked Telstra under its obligations in the Privacy Act to hand over all the metadata related to his mobile phone. Telstra responded that Grubb could only get access to information contained in his mobile phone bill, and Grubb filed a complaint with Privacy Commissioner Timothy Pilgrim.