One method we've been using is looking for multiple failed logins from a single IP.
sourcetype="some source where login
attempts are logged" ipaddress!=10.*
NOT Succeeded| stats
distinct_count(loginname) AS
logincount by ipaddress | where
logincount > 10
IE: For all ips not in our local subnet and without a "Succeeded" message in our application access log, provide stats on each login grouped by ipaddress, and only show me the results where 10 or more accounts had unsuccessful access attempted to.
Another method:
If you know the site that is phishing user data, you can also use Splunk to create a honeypot. To do this setup a saved search & alert on some sort of input value known only to you, and then use that value on the site. If the value you provided is attempted, you'll get an alert (hopefully with the data necessary to mitigate further). This is helpful as often the site phishing the data is not the IP that is attempting to re-use and exploit the data.
