The service might also provide version information on connection. This helps determine specific vulnerabilities. Rulesets use IP addresses and machine names. Sending only the first packet of a handshake is enough to tell if a service is running. This event frequently occurs on the Internet.
Possible strobes come from the same client and to different server ports.
Vulnerable Network Applications On Internet servers, many network services run with full privileges. Programming defects make these services vulnerable to attack. Read the CERT advisories. Get newer versions. If a server places trust in a client's domain name, this trust can be subverted.