Morning Money Memo:

Nobody said it would be easy. The brave new world of virtual currency trading has been hit by the apparent collapse of one of the world's largest bitcoin exchanges. Prices plunged to a three-month low Tuesday.

The virtual currency is popular among tech enthusiasts, libertarians and investors because it allows people to make transactions and exchange money without involving banks, credit card issuers or other third parties. Criminals like bitcoins for the same reasons.

Japanese and U.S. regulators are ramping up investigations into how bitcoins are traded.

A coalition of virtual currency companies says Tokyo-based Mt. Gox went under after secretly racking up catastrophic losses.

Mt. Gox's website wasn't functioning Tuesday. That follows the resignation Sunday of its CEO from the board of the Bitcoin Foundation, a group seeking legitimacy for the new form of money. The exchange had imposed a ban on withdrawals earlier this month.

Bitcoin investors who put their money in Mt. Cox might be out of luck. Unlike banks where deposits are insured, deposits in this sort of closed exchange might not be protected from a collapse.

The U.S. tax code might be a mess, but don't expect an overhaul soon. Blame partisan gridlock in Congress.

Michigan Rep. Dave Camp, the Republican chairman of the House Ways and Means Committee, is to outline his plan for overhauling the tax code today.

The blueprint has been three years in the making and would lower the top income tax rate to 25 percent from nearly 40 percent and impose a new 10 percent tax on some earned income above $450,000. But in the Senate, Minority Leader Mitch McConnell, R-Ky., has already pronounced the legislation dead.

Senate investigators are out with blistering findings about Switzerland's second-largest bank. A report says Credit Suisse helped U.S. tax cheats hide billions of dollars in assets. The findings come after a two-year investigation by the Senate Permanent Subcommittee on Investigations.

Target's data breach was expensive. The discount retailer says the November-December theft was a big reason 4th quarter profits dropped 46 percent. Sales during the important holiday shopping season plunged 5.3 percent.

Federal regulators have issued an emergency order requiring tests of crude oil before it's shipped by rail. This comes in response to a string of train explosions and fires since last summer. The Federal Railroad Administration says it also is prohibiting shippers from transporting oil using the least-protective packing requirements.

Shippers already had to classify oil shipments based on their risk for explosion or fire, but federal investigators found that many were being misclassified as less dangerous. The order requires testing for classification before shipment.

Richard Davies Business Correspondent ABC News Radio abcnews.com Twitter: daviesnow 212-456-5100