Heartbleed (OpenSSL vulnerability)
Kind of surprised someone hasn't already made a topic about this one. I know a lot of folks here run Linux at home and/or at work.
Anyways, if you're running OpenSSL anywhere, you should definitely check to see if you're running a version with the bug, and update if so. It's a nasty one.
Most of the major Linux distros came out with updates yesterday or this morning. If your router is running some sort of embedded linux, you may want to keep your eye open for a firmware update, especially if you allow remote management.
Test a server for the issue:
AWS's ELB is affected:
Edited for more info and links.