• Inability to upgrade to any version that changes how users are stored
• Admin pages don't load because they attempt to query the users profile tables
• SQL Queries, including scheduled DNN tasks, time out
• DNN File manager not functioning properly
• Site frequently loses connection to database - showing "Page unavailable" or "Error Connecting to Database"

<system.webServer>
  <security>
    <requestFiltering>
         <denyQueryStringSequences>
              <add sequence="ctl=Register" />
              <!--added by PowerDNN due to Registration exploit-->
        </denyQueryStringSequences>
    </requestFiltering>
  </security>
</system.webServer>   

1. Open Microsoft SQL Server Management Studio, and start a New Query
2. Enter the following text, replacing databasename with the name of the database for the website in question.  Replace rest of the bolded words with the appropriate pieces of information to restrict the deletion. 

   use DatabaseName
   UPDATE UserPortals
       SET IsDeleted='True'
       WHERE 
         UserID != '2'
         AND UserID !='OtherUserID'
         AND PortalId = 'The ID # of the portal you want to target for removal'
         AND CreatedDate >= 'The date fake users started registering, Year-Month-Day'
         AND UserID NOT IN( 
           SELECT UserID FROM Users 
           WHERE LOWER(Username) = LOWER('username')
         )

3. Once entered, Execute the Query by pressing the red exclamation point or hitting F5
4. This will run through the database and mark each user who wasn't specified as deleted.  They'll still show up in the user list, but their name will be crossed out.  This is a pretty safe query to adjust, as we can just set them back to IsDeleted='False' if the results don't match what was expected.

• use databasename:   This tells SQL which database to run the query on.  replace databasename with the name of your database.
• UPDATE UserPortals:  UserPortals is the master table of users that belong to a portal (all users that are not SuperUsers)
• SET IsDeleted='True':  This "Soft Deletes" the any user selected by the query
• WHERE ... :  Sets the conditions for selection
• UserID != '2' :  Explicitly excludes the default DNN "admin" account.  Not necessary, but many people like to use their admin account.
• AND ... : Allows you to have multiple conditions, you'll need one before each new condition.  You can have as many of each condition as you want, except for CreatedDate (see Advanced Section).
• UserID !='otherUserID' : By replacing otherUserID with an ID number, we can save another admin accounts that we know that ID for.  You can add as many of these as you want to save multiple users.
• AND PortalId='###':  This restricts the deletion to only a single portal.  Or if you add multiple of these, the portals you select.  You can find the Portal ID in Host > Site Management or Host > Portals, depending on your version.
• AND CreatedDate >= 'date':  This restricts the deletion to only users after a certain date.  If you don't care about when they were created, just remove this line.
• AND UserID NOT IN(...):  This looks a bit more complicated, but what it's doing is looking at another table to compare the name you put in with the name of each user before it marks it as deleted.  By doing this, you can specify a user to not delete by name.  For example, if you have an admin named "John" and can't get into the site to bring up the ID for the other criteria, you can put "john" into the username spot here to make sure that user doesn't get deleted.

WHERE convert(date, CreatedOnDate) = convert(date,'20141001')

use DNN_Database
UPDATE UserPortals
    SET IsDeleted='True'
    WHERE 
        convert(date, CreatedOnDate) >= convert(date, '20140601')
        AND PortalID = '6'
        AND UserId = '2'
        AND UserID NOT IN(
            SELECT UserId FROM Users
            WHERE Lower(Username) = Lower('jon')
            )
        AND UserID NOT IN(
            SELECT UserId FROM Users
            WHERE Lower(Username) = Lower('CaRlA')
            )
        AND convert(date, CreatedOnDate) <= convert(date, '20140815')

1. Create a PowerShell script in C:\temp\ named "Find-Or-Remove-Empty-Dirs.ps1".
2. Open the file in PowerShell ISE or Notepad++
3. Copy the following script into the file and save it

   <#
   .SYNOPSIS
   Svendsen Tech's generic script for removing empty directories from a
   directory tree structure.
   
   Finds or removes/deletes empty directories recursively from the drive or
   directory you specify.
   
   You will need to use the -VerifyNoEmpty parameter or multiple
   runs to get rid of nested empty directories. See the -VerifyNoEmpty parameter's
   description for further details.
   
   This isn't the most efficient approach as the ones I can think of seem to
   increase the script's complexity considerably. It should be useful for a
   multitude of use cases.
   
   Author: Joakim Svendsen
   
   .PARAMETER Path
   Required. Base root path to iterate recursively.
   .PARAMETER Find
   Default behaviour where it just prints. Overrides -Remove if both are specified.
   .PARAMETER Remove
   Removes all empty dirs (as in actually deletes them with Remove-Item).
   .PARAMETER VerifyNoEmpty
   Makes the script run until no empty directories are found. This is in order
   to handle nested empty directories, as in a directory that currently only
   contains an empty directory would be empty after the first run/iteration and
   need to be remove in a subsequent run. Specifying this parameter causes the
   script to run until it's done a complete run without finding a single empty
   directory. This might be time-consuming depending on the size of the directory
   tree structure.
   
   If there is an error while deleting a directory, it will not run again, to
   avoid an infinite loop.
   #>
   
   param(
       [Parameter(Mandatory=$true)][string] $Path,
       [switch] $Find,
       [switch] $Remove,
       [switch] $VerifyNoEmpty
       )
   
   Set-StrictMode -Version 2.0
   $ErrorLog   = 'remove-empty-dirs-error.log'
   
   ######## START OF FUNCTIONS ########
   
   function Iterate-And-Remove-Empty-Dirs {
       
       $FoundEmpty = $false
       
       Write-Host "Iterating '$Path'"
       
       Get-ChildItem -Force -Recurse -Path $Path -ErrorAction SilentlyContinue | Where-Object { $_.PSIsContainer } | ForEach-Object {
           
           if ($Find -or -not $Remove) {
               
               if (-not (Get-ChildItem -Force $_.FullName)) {
                   
                   # Directory should be empty
                   $_.FullName + ' is empty'
                   
               }
               
           }
           
           # This is the dangerous part
           elseif ($Remove) {
               
               if (-not (Get-ChildItem -Force $_.FullName)) {
                   
                   $FoundEmpty = $true
                   
                   # Directory should be empty
                   Remove-Item -Force $_.FullName
                   
                   if (-not $?) {
                       
                       Write-Host -ForegroundColor Red "Error: $(Get-Date): Unable to delete $($_.FullName): $($Error[0].ToString))"
                       "Error: $(Get-Date): Unable to delete $($_.FullName): $($Error[0].ToString))" | Out-File -Append $ErrorLog
                       
                       $FoundEmpty = $false # avoid infinite loop
                       
                   }
                   
                   else {
                       
                       Write-Host -ForegroundColor Green "$(Get-Date): Successfully deleted the empty folder: $($_.FullName)"
                       
                   }
                   
               }
               
           }
           
       } # end of ForEach-Object
       
       $FoundEmpty
       
   } # end of function Iterate-And-Remove-Empty-Dirs
   
   ######## END OF FUNCTIONS ########
   
   if (-not (Test-Path -Path $Path -PathType Container)) {
       
       "The specified path does not exist. Exiting with code 1."
       exit 1
       
   }
   
   if ($Remove -and $VerifyNoEmpty) {
       
       $Counter = 0
       
       while (($OutsideFoundEmpty = Iterate-And-Remove-Empty-Dirs) -eq $true) {
           
           $Counter++
           Write-Host -ForegroundColor Yellow "-VerifyNoEmpty specified. Found empty dirs on run no ${Counter}. Starting next run."
           
       }
       
       $Counter++
       
       Write-Host "Made $Counter runs in total"
       
   }
   
   else {
       
       Iterate-And-Remove-Empty-Dirs
       
   }

   The script comes from here, but is included in the article just in case that site goes down.
4. Save the script and exit
5. Open PowerShell and run the following command,

   Set-ExecutionPolicy

6. When prompted, enter the following

   RemoteSigned

   y

    
7. Now run these commands, changing <SiteName> to the site you are working on and <PortalNumber> to the number of the portal that the users are registered to

   cd C:\temp\

   .\Find-Or-Remove-Empty-Dirs.ps1 -Path C:\inetpub\vhosts\<SiteName>\httpdocs\Portals\<PortalNumber>\Users -Remove -VerifyNoEmpty

8. After the script has run successfully, switch powershell back to Restricted mode by using the following commands:

   Set-ExecutionPolicy

   Restricted

   y