The remote host is missing an update to qemu-kvm announced via advisory DSA 2230-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%202230-1

Two vulnerabilities have been discovered in KVM, a solution for full virtualization on x86 hardware: CVE-2011-0011 Setting the VNC password to an empty string silently disabled all authentication. CVE-2011-1750 The virtio-blk driver performed insufficient validation of read/write I/O from the guest instance, which could lead to denial of service or privilege escalation. The oldstable distribution (lenny) is not affected by this problem. For the stable distribution (squeeze), this problem has been fixed in version 0.12.5+dfsg-5+squeeze1. The unstable distribution (sid) will be fixed soon. We recommend that you upgrade your qemu-kvm packages.