We currently use JIRA for customer support.
We do have over 1500 different people/customers with an account. Using groups and security level to divide these customers in different groups. So customers working for the same company could see each others issue and not the issues from other companies.
Now we are thinking about moving to JIRA Service Desk, but I am not able to find any functionality to use security levels of some sort for customers.
This is one of our main requirements for a support system,