Vista - Event viewer error

This is another error that is happening 4-5 times a day.....What do I have to
do to fix it?

Log Name: System
Source: Microsoft-Windows-Windows Defender
Date: 3/3/2007 11:01:30 AM
Event ID: 3004
Task Category: None
Level: Warning
Keywords: Classic
User: N/A
Computer: Irv-PC
Description:
Windows Defender Real-Time Protection agent has detected changes. Microsoft
recommends you analyze the software that made these changes for potential
risks. You can use information about how these programs operate to choose
whether to allow them to run or remove them from your computer. Allow
changes only if you trust the program or the software publisher. Windows
Defender can't undo changes that you allow.
For more information please see the following:
Not Applicable
Scan ID: {1B1A7A33-A51C-47E1-BD80-5B1B7C6A778D}
User: Irv-PC\Irv
Name: Unknown
ID:
Severity ID:
Category ID:
Path Found: ieext:HKLM\Software\Microsoft\Internet
Explorer\Extensions\{724d43aa-0d85-11d4-9908-00400523e39a}
Alert Type: Unclassified software
Detection Type:
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
<System>
<Provider Name="Microsoft-Windows-Windows Defender"
Guid="{11CD958A-C507-4EF3-B3F2-5FD9DFBD2C78}" EventSourceName="WinDefend" />
<EventID Qualifiers="0">3004</EventID>
<Version>0</Version>
<Level>3</Level>
<Task>0</Task>
<Opcode>0</Opcode>
<Keywords>0x80000000000000</Keywords>
<TimeCreated SystemTime="2007-03-03T16:01:30.000Z" />
<EventRecordID>16785</EventRecordID>
<Correlation />
<Execution ProcessID="0" ThreadID="0" />
<Channel>System</Channel>
<Computer>Irv-PC</Computer>
<Security />
</System>
<EventData>
<Data Name="Product Name">%%827</Data>
<Data Name="Product Version">1.1.1505.0</Data>
<Data Name="Scan ID">{1B1A7A33-A51C-47E1-BD80-5B1B7C6A778D}</Data>
<Data Name="Unused">
</Data>
<Data Name="Unused">
</Data>
<Data Name="Unused">
</Data>
<Data Name="Unused">
</Data>
<Data Name="Domain">Irv-PC</Data>
<Data Name="User">Irv</Data>
<Data Name="SID">S-1-5-21-1903812106-2428839669-1432131728-1000</Data>
<Data Name="Threat Name">Unknown</Data>
<Data Name="Threat Id">
</Data>
<Data Name="Threat Severity">
</Data>
<Data Name="Threat Category">
</Data>
<Data Name="FWLink">%%832</Data>
<Data Name="Path Found">ieext:HKLM\Software\Microsoft\Internet
Explorer\Extensions\{724d43aa-0d85-11d4-9908-00400523e39a}</Data>
<Data Name="Threat Classification Index">0</Data>
<Data Name="Threat Classification">%%807</Data>
<Data Name="Unused">
</Data>
<Data Name="Unused">
</Data>
<Data Name="Detection Type Index">
</Data>
<Data Name="Detection Type">
</Data>
</EventData>
</Event>