In most of the bonus programs for sharing miles, by sharing miles back and forth extra miles can effectively be manufactured. For example, A shares 50K miles with B but B gains 100K miles, then B shares 50K miles with A who gains 100K miles - A and B each gain 50K miles for minimal cost. Freezing the account(s) involved is the first step of an audit. It doesn't mean you've done anything wrong, only that they're going to take a look at the activity. If you've complied with the rules of the promo you should have nothing to worry about unless you need access to the account miles before the audit is completed.
The same is true for getting an award ticket for someone else, especially if they have a different last name. There is the occasional case of someone selling award tickets and that's what they're looking for evidence of.
Jim