The answer to this question is context sensitive.
If there is no copyright in the data, you can do anything. The question is, how do you know if copyright subsists in the data or not? Thats a question for another day.
If copyright does subsist in the data (and lets say that a lot of data is in this category), and you are an employee of State or Federal Government, you can probably use it internally to your agency, but you should not publish it. More importantly, other people will not be able to reuse it outside of government.
If you are not in State or Federal Government, you are subject to the normal rules of copyright, and consequently, no licence means ‘all rights reserved’. 'All rights reserved ’ means you cannot do anything with the data that involves one of the copyrights (reproduction, communication or publication) unless your reuse falls within one of the Fair Dealing provisions in the Copyright Act, or you are not making a “substantial reproduction” of the data. Substantial in Australia is defined by reference to both a quantitative and qualitative test. You may reproduce only a small part, but it may be the most important part.
So yes, Maree is correct! By far the best option is to ask the data publisher to apply a licence to it, and if they want it to be open data it should be a Creative Commons Attribution 4.0 Licence, or, if copyright doesn’t subsist, the Creative Commons Public Domain Mark… If they are unsure, they should apply the CC licence.
The attribution issue is a separate matter. If a licence is applied it should also be made clear by the licensor how they wish to be attributed. If the data is in the public domain, strictly there is no need to attribute the data, however courtesy and domain specific norms (academic for example), usually dictate some form of citation / attribution.
There is more information about this on the AusGOAL website (which is being refreshed at the moment).