MS SQL Server 2005 Event ID: 18456 / Event ID: 18454

Hi Experts!

I got this information inside Event Viewer -> Windows Logs -> Application

Log Name:      Application
Source:        MSSQLSERVER
Date:          5/12/2013 12:41:22 AM
Event ID:      18456
Task Category: (4)
Level:         Information
Keywords:      Classic,Audit Failure
User:          N/A
Computer:      Keywordserver
Description:
Login failed for user 'sa'. [CLIENT: <local machine>]
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="MSSQLSERVER" />
    <EventID Qualifiers="49152">18456</EventID>
    <Level>0</Level>
    <Task>4</Task>
    <Keywords>0x90000000000000</Keywords>
    <TimeCreated SystemTime="2013-05-11T16:41:22.000Z" />
    <EventRecordID>204233209</EventRecordID>
    <Channel>Application</Channel>
    <Computer>Keywordserver</Computer>
    <Security />
  </System>
  <EventData>
    <Data>sa</Data>
    <Data> [CLIENT: &lt;local machine&gt;]</Data>
    <Binary>184800000E0000000E0000004B004500590057004F00520044005300450052005600450052000000070000006D00610073007400650072000000</Binary>
  </EventData>
</Event>

afterwards it is like this:

Log Name:      Application
Source:        MSSQLSERVER
Date:          5/12/2013 12:40:55 AM
Event ID:      18454
Task Category: (4)
Level:         Information
Keywords:      Classic,Audit Success
User:          N/A
Computer:      Keywordserver
Description:
Login succeeded for user 'sa'. Connection: non-trusted. [CLIENT: <local machine>]
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="MSSQLSERVER" />
    <EventID Qualifiers="16384">18454</EventID>
    <Level>0</Level>
    <Task>4</Task>
    <Keywords>0xa0000000000000</Keywords>
    <TimeCreated SystemTime="2013-05-11T16:40:55.000Z" />
    <EventRecordID>204233208</EventRecordID>
    <Channel>Application</Channel>
    <Computer>Keywordserver</Computer>
    <Security />
  </System>
  <EventData>
    <Data>sa</Data>
    <Data> [CLIENT: &lt;local machine&gt;]</Data>
    <Binary>164800000A0000000E0000004B004500590057004F00520044005300450052005600450052000000070000006D00610073007400650072000000</Binary>
  </EventData>
</Event>

I noticed that this occurs every 30 seconds.

I also tried to check the SQL Server 2005 database to test login for "sa". It seems good but I'm bothered with this information.

Thank you.