Creation of a Hidden Local User Account

## Triage and analysis

### Investigating Creation of a Hidden Local User Account

Attackers can create accounts ending with a `$` symbol to make the account hidden to user enumeration utilities and
bypass detections that identify computer accounts by this pattern to apply filters.

This rule uses registry events to identify the creation of local hidden accounts.

#### Possible investigation steps

- Identify the user account which performed the action and whether it should perform this kind of action.
- Investigate the script execution chain (parent process tree).
- Investigate other alerts related to the user/host in the last 48 hours.

### False positive analysis

- This activity is unlikely to happen legitimately. Benign true positive (B-TPs) can be added as exceptions if necessary.

### Response and remediation

- Initiate the incident response process based on the outcome of the triage.
- Quarantine the involved host to prevent further post-compromise behavior.
- Delete the hidden account.
- Review the privileges of the involved accounts.

## Config

If enabling an EQL rule on a non-elastic-agent index (such as beats) for versions <8.2, events will not define `event.ingested` and default fallback for EQL rules was not added until 8.2, so you will need to add a custom pipeline to populate `event.ingested` to @timestamp for this rule to work.