On April 4, Canonical published in a security notice details about Libav vulnerabilities for its Ubuntu 12.10 and Ubuntu 12.04 LTS operating systems.
According to Canonical, Libav could have been made to crash or run programs as the users log in if it opened a specially crafted file.
It was discovered that Libav incorrectly handled certain malformed media files. If a user were tricked into opening a crafted media file, an attacker could cause a denial of service via application crash, or possibly execute arbitrary code with the privileges of the user invoking the program.
The security flaws can be fixed if you upgrade your system(s) to the latest libavformat53 and libavcodec53 packages, specific to each distribution. To apply the update, run the Update Manager application.
In general, a standard system update will make all the necessary changes. A system restart will not be necessary to implement the changes.