This question comes up quite often. The answer is that no, they...

1. This question comes up quite often. The answer is that no, they would not need to make any announcement about an "approach". And they would not, in fact, do so.
   The ASX listing rules do demand "continuous disclosure" of relevant matters in Rule 3.1. But Rule 3.1A.1 qualifies that duty by saying it does not apply in certain situations. Here are the relevant Rules:
   
   ”3.1 Once an entity is or becomes aware of any information concerning it that a reasonable person would expect to have a material effect on the price or value of the entity’s securities, the entity must immediately tell ASX that information.

   
   

   3.1A Listing rule 3.1 does not apply to particular information while each of the following requirements is satisfied in relation to the information:

   
   

   3.1A.1 One or more of the following 5 situations applies:

   • It would be a breach of a law to disclose the information;
   • The information concerns an incomplete proposal or negotiation;
   • The information comprises matters of supposition or is insufficiently definite to warrant disclosure;
   • The information is generated for the internal management purposes of the entity; or
   • The information is a trade secret; and

   
   

   3.1A.2 The information is confidential and ASX has not formed the view that the information has ceased to be confidential; and

   
   

   3.1A.3 A reasonable person would not expect the information to be disclosed.”

   
   

   Note that all three conditions need to be fulfilled. If any one of them is not fulfilled, the information must be disclosed.
   
   So, just to work through an example, assume someone has "approached" the company and said something like: "Just between ourselves, if we were to offer to buy your company for X dollars a share, how would you feel about that? Would you be prepare to recommend that your shareholders accept an offer in those terms?" There might then be negotiations about what figure would get the board's backing or about other terms. Note that no actual offer has yet been made. This would 1: concern an incomplete proposal or negotiation (3.1A.1, second bullet); and 2: it would be confidential (3.1A.2); and 3: a reasonable person would not expect it to be disclosed (3.1A.3). So the company would not be required to disclose it and would not do so because disclosure in those sorts of circumstances would make negotiations on anything impossible.
   
   It would be different if an actual offer had been made because that would need to be put to the shareholders. But that is not how these things are done. Negotiations would initially take the form of "I am not actually saying X but if I did say X, how would you respond?" An agreement with the company would always be preferred because the suitor would want the target board's endorsement and may well want other things, such as key personnel to stay in their roles. Only if no agreement was forthcoming might the suitor make an actual offer and force the target board to announce it and put it to their shareholders.
   
   Other posters have noted, correctly in my view, that the company's announcement does not actually say that no approaches have been made. I would not be surprised if there had been correspondence in the background to enable the ASX to decide whether the it should form the view that some information has ceased to be confidential (3.1A.2) and should, therefore, be disclosed. Maybe, maybe not. If I were the ASX, I would have asked the company questions directed to seeing whether the press had got hold of enough information to mean things had ceased to be confidential and needed to be disclosed in the interests of a fair and informed market. That would all happen pretty quickly, so the fact we have had no follow up announcement suggests the ASX has not formed that view. But it is not impossible we could find ourselves in a trading halt in the morning pending some further announcement.