How to prevent Brut force attack?

Hello and TYIA,

It looks like one of our Windows 2008 SBS is being attacked.  In the security log, I see about 1400 event ID 4625 Audit Failures in the last 24 hours.  They are all coming from different Ports and from IP addresses and use different usernames. What is the best way to stop and prevent these attacks.

Although this is an SBS, we are not using the Exchange or the SharePoint services.  We are only using it as an AD/File/Print server

Thank you,

dp

dp