On January 28, in a security notice Canonical published details about FFmpeg vulnerabilities for its Ubuntu 10.04 (Lucid Lynx) operating system.
According to Canonical, FFmpeg could be made to crash or run programs as your login if it opened a specially crafted file.
It was discovered that FFmpeg 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.
For a more detailed description of the security problems, you can visit Canonical's security notification.
Users can simply fix the security flaws by upgrading the operating systems to the FFmpeg packages specific to each distribution.
A normal system update, executed with the Update Manager, will implement all the necessary changes. A complete system restart is not necessary.