Still interested in getting this done. Not looking for freebees - we have a budget for this project.

Thanks Matt but there is nothing I can do with that. I was hopeing for a plug in that can do it. 

I installed  bulk user admin plugin but I would have to tick over 1000 times. I would like a select all optition . 

@Luis: I'm afraid a "Select all" option might not necessarily help you much either. This would delete ALL accounts. Even if the "Select all" option would only select for example 10, 20 or 100 currently displayed users how do you know that there's no valid user in between them? Is there any criteria that allows you to say for sure that an account is a spam account? For example are the spammer accounts already banned? Based on such a criteria it would be easy to write a little script that deletes the banned users - and only the banned users.

@luis : if you want to remove all the users with out any filter, then why cant you start with a fresh install?

how do I do a mass delete of all accounts except my own admin account

 

If that's your goal, then delete the database and start over.

Start with a new install and use this plugin for admin moderation http://community.elgg.org/plugins/875414/1.0/user-validation-by-admin-for-18x

For mass deletion of accounts you can also try this plugin: https://github.com/brettp/Bulk-User-Admin. It will allow you to delete users also based on the email domains they used for registration, so you should be able to delete a lot of users quite fast. It also allows to delete several users selected at once.

If you delete a user account all the stuff they added (e.g. blogs) will get removed, too.

For setting up a website for a closed community you can surely start by using the plugin suggested by Team Webgalli. Depending on the number of members to expect for the site you can also disable user registration completely (advanced settings). Maybe it would be easier to create the accounts manually (as admin you can create new accounts), if there are not too many to be created.

Independent from the account registration I would suggest to also allow content to be viewed by logged-in users only (advanced settings). This might at least reduce the number of spam accounts created a bit. If you can't disable registration of new accounts, you should install a few anti-spam plugin (Spam Filter, Spam Throttle, Honeypot), to reduce the spam accounts as best as possible.