Morgan Stanley Shares Plunged: What You Need to Know

Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of investment bank Morgan Stanley (NYS: MS) were swooning today, falling as much as 12% in intraday trading on the news that Greece is calling a referendum vote on the latest bailout agreement.

So what: Morgan Stanley is widely seen as the major U.S. bank most exposed to the turbulence in the eurozone, and those concerns may have been stoked further after the eurozone-bet-linked bankruptcy of broker MF Global (NYS: MF) .

Greece's call for a referendum vote on the bailout package could put the country's rescue package at risk and potentially lead to a disorderly default for the country. The latter could lead to market dislocations and increased bets against other fiscally troubled countries like Italy and Spain, which would hurt exposed banks like Morgan Stanley.

Now what: With the disaster of MF Global fresh in investors' minds, they may be being particularly harsh with Morgan Stanley's stock today. Notably, though, Morgan Stanley doesn't have the same level of exposure that MF Global did, and also has a broader business and capital base to protect it from a similar fate. Now is that a guarantee that the worst-case scenario couldn't come true for the bank? Unfortunately, no. While it may be a long shot, the unraveling of MF Global is a reminder that when you depend on the confidence of counterparties to stay afloat, a situation can go from bad to worse very rapidly.

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