What is happening

If you are using an old version of Bitcoin-Qt (or bitcoind, the server bitcoin software), you must either upgrade to version 0.8.0 or later before May 15, 2013, upgrade to an up-to-date "backport" release, or modify a file and restart bitcoin to work around a bug with the old software.

This bug does not affect any bitcoins you already have, but if you do nothing you will be out of sync with the rest of the Bitcoin network and will be unable to receive bitcoins (payments sent to you will look like they never get confirmed, or will be confirmed very slowly). You also risk being the victim of a "double-spend" attack, where somebody sends you bitcoins that the rest of the network would reject as invalid.

We recommend that you upgrade to version 0.8.1 before the 15th of May to avoid any issues. If you are a solo miner or mining pool operator, please see the the notes at the end of this page for how to upgrade safely.