I would strongly suggest that you consult your textbook and/or your class notes as there are different ways to define these various crimes. For example, this link does not say that internet fraud is different from hacking or identity theft. Instead, it says that the latter two crimes are types of internet fraud. You should check to see how your text says that they differ. In my view, the best answer is that hacking and internet extortion are different from internet fraud while identity theft (if committed through use of the internet) is a type of internet fraud. I would also say that the only difference between fraud and internet fraud is that internet fraud must be done using the internet.
Fraud is a crime in which a person steals from or otherwise harms another person (to the first person’s advantage) through false statements or deception. Internet fraud is simply fraud committed through the use of the internet. There are many kinds of internet fraud.
One common cybercrime is hacking. Hacking consists of gaining unauthorized access to a computer network. This is typically accomplished over the internet. I do not see it as a kind of fraud because it does not really involve false statements or deception. Instead, it more usually involves finding flaws in computer security and accessing computer systems through those flaws. It is possible to say that hacking is fraud if the hacker uses stolen passwords (because using someone’s password is a false statement that you are they) but that is something of a stretch in my view.
Internet extortion happens after hacking. The hacker/extortionist essentially holds the computer network for ransom. They take the information they have gained, or the control they have over the network, and demand money or other considerations. If they are paid, they will return control of the network to the rightful owner. This is not a deception and therefore it is not fraud.
Identity theft is a type of internet fraud. It can also be accomplished through hacking. Hackers can steal the personal information that is stored on computer networks. They can then use that information to pretend to be the people whose information it is. When they do this, they are making false statements. They are claiming to be someone that they are not. When they do this, they are committing fraud.
Thus, Internet fraud is one type of fraud and identity theft is one type of internet fraud. Hacking and internet extortion are, in my view, different things, but some authorities feel that they are the same. Please check to see what your own class materials have to say on this issue.