Getting emails with _HASHCASH_ADMINMAILHEADER in subject line

[lapple]

Using Joomla 1.5.4
SecurityImages 5.0.0RC1
plugin_system_securityimages5.0.0RC1
Joomla_1.5.4-Stable-Full_PackageForSecurityimages5.0.0


If I look at security images logs they coincide with a Joomla contact form.   

The email body contains a table of information (which i will sent on request)
Is there a way to stop this?  Is this just a notification of a hack attempt?. 
From reading about it in 2006 this was a sign of being hacked. 

please enlighten me or point me in a direction for a fix

Thank you

[cedricwalter]

not an attack but you have more than 100 captcha failed attempt recorded in your database.

Either

Log spam submission to off
OR
Notify admin: to off to avoid receiving emails
OR
increase "Notify when table size:" from 100 to ?
OR
empty the DB logs by "View Logs file", then click on "Empty logs"