This is the exact problem and scenario that The Open Port and Vulnerability Detector (OPVD) was designed to solve. It is part of Hurricane Labs’ Continuous Monitoring Service known as Hurricane Defense.

OPVD provides the following:

• Watch for new or previously unknown machines to pop up – will interrogate them for open ports and vulnerabilities.
• Critical and high level vulnerabilities will generate an alert – one of our engineers will contact you.
• New or previously unknown ports will generate an alert – can be baselined so that you don’t get alerted on them again.
• Previously examined ports will still be tested for vulnerabilities – providing you the ultimate coverage.