As mentioned yesterday, Frontier is upgrading Elite Dangerous and they warned everyone to finish their open missions because they were about to get wiped. Although the maintenance window opened (Frontier is in UK) about 3 hours ago, but they are expecting it to be a a full Nine hours in duration, which will slide into early afternoon here in the U.S. Keep an eye posted on their twitter feed for updates. Once the window ends, you can probably give it a few hours before the first money exploit surfaces, then we have a new mad rush to get as much cash as possible before they patch it. Happy Exploration!
[EDIT: DAN] The patch notes were just released and they are significant (hence teh Nine hour maintenance window I guess). Way to much to print here, so check them out in the Frontier Forums.