Mt. Gox has stopped bitcoin deposits and all internal bitcoin transfers for a short site maintenance update, roughly from 6pm to 12am Japan time on 15th February.
According to a notice posted on Gox's News page, the downtime is part of its implementation of a solution to the 'transaction malleability' issue that has seen the exchange halt all external bitcoin withdrawals and face criticism from some sectors of the bitcoin economy.
The downtime probably won't affect too many users. With Mt. Gox's bitcoin price now hovering around the $342 mark (at least $300 below the CoinDesk BPI) and the exact situation regarding bitcoin withdrawals still unknown, it's not very likely people are trying to move coins into the exchange right now. Internal transfers can probably also wait a short while.
The announcement continued that the 6-hour timeframe was approximate only, and could be shortened or lengthened if required. It also said the new system would need to have "extensive testing" before bitcoin withdrawals could begin again, and that a further update would be published on Monday (17th February).
It also mentioned that other exchanges have taken their own steps to address the transaction malleability issue, which CEO Mark Karpeles claims is a serious flaw in the bitcoin protocol. The issue was first noticed in 2011 but was not considered a high priority by bitcoin's core developers - at least until Mt. Gox's current problems began.
Other exchanges have posted statements saying they are not affected by transaction malleability, though Bitstamp, one of the world's most popular exchanges, also briefly halted bitcoin withdrawals after a "massive and concerted" DDoS attack affected it and numerous others. It has since resumed regular operations.
Image: Mt. Gox logo