The remote host is missing an update to qemu-kvm announced via advisory DSA 2241-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%202241-1

Nelson Elhage discovered that incorrect memory handling during the removal of ISA devices in KVM, a solution for full virtualization on x86 hardware, could lead to denial of service of the execution of arbitrary code. For the stable distribution (squeeze), this problem has been fixed in version 0.12.5+dfsg-5+squeeze2. For the unstable distribution (sid), this problem will be fixed soon. We recommend that you upgrade your qemu-kvm packages.