[Serusers] Strange "sip scans" from "qualsys.com"

[Arnd Vehling]

Hi,

while strolling through my sip server logile ive came accross some 
strange unauthorized sip messages originating from "scan.qualsys.net":
(ip address has been logged to)

---
OPTIONS sip:scan.qualys.com SIP/2.0
Via: SIP/2.0/UDP scan.qualys.com:5060;branch=z9hG4bKnashds7
Max-Forwards: 70
To: Foo <sip:foo at scan.qualys.com>
From: Foo <sip:foo at scan.qualys.com>;tag=456248
Call-ID: 843817637684230 at 998sdasdh09
CSeq: 1826 OPTIONS
Accept: application/sdp
Content-Length: 0
---

These packets could be found in ALL our SIP Proxy logs and they
are clearly unauthorized.

Has anyone a idea what this could be about or found similiar
sip messages in his log?

-- Arnd