Earlier today both Debian and Ubuntu maintainers announced a serious security issue with both Open SSH and Open SSL.
There is, of course, a post about it on SlashDot, but if you’d rather skip the crud (ie. some of the rather inane comments) and are running a Debian (or derivative system such as Ubuntu) do a dist-upgrade as soon as you can.
If you’re using SSH keys you’ll need to generate fresh ones, as any keys currently “in the wild” maybe vulnerable to brute force attacks.