When Telstra offered its mobile customers unlimited data for two separate days this year as compensation for network outages, some customers took it as a challenge to download as much as they possibly could in one day.

On Sunday, 27-year-old Sydney resident John Szaszvari outdid himself and everyone else by ploughing through almost a whole terabyte of data.

That's more than double what he managed during the first free data day in February – an already mammoth 425GB.

Szaszvari's data guzzling even caught the attention of Telstra chief operating officer Kate McKenzie, who mentioned his heroic 994GB effort during a speech at the CommsDay conference in Sydney.