How vulnerable is your mutual fund to the ongoing mortgage meltdown? In this series, BloggingStocks contributor Lita Epstein, author of more than 20 books including Trading for Dummies and The Complete Idiot's Guide to Improving Your Credit Score, digs into mutual funds' holdings looking for securities with exposure to the currently shaky credit markets.

After reviewing funds from Bank of America, JPMorgan, and Fidelity, companies that have been mentioned in some of the SIV bailout stories, I looked to see if other bond mutual funds also had significant exposure to the credit markets tied to this mortgage and asset-backed securities mess. While I can't guarantee that I located all the ones with significant exposure to this mess, here are some key players:

Eaton Vance Low Duration A has the riskiest position by far of all the ones I look at this morning. As of 04/30/07, this fund held 79.93% of its assets in mortgage pass-through securities. More than 75% of its holdings are in bonds rated BB and B. Its yield of 5.5% certainly doesn't justify this risk. If you are holding this fund, you could find a safer bet with similar yields.

As of 9/30/2007, Credit Suisse Short Duration A held 15.43% of its assets in mortgage pass-through securities, 13.86% in collateralized mortgage obligations, and 12.82% in asset-back securities. That's slightly more than 40% of its portfolio in the type of credit markets now showing signs of trouble.

Got Crocs? If you're a student at Thompson Elementary in North Andover, Mass., you'd better leave them at home along with your bubble gum, guns and flip-flops. Principal John McAller has banned Crocs and all other footwear that does not completely cover his students' feet. He says he's "looking out for his students' well-being on the playground and in the event of a fire emergency," according to Boston's WHDH-TV.

Sure, one elementary school banning the wildly popular resin footwear might seem like a nonsensical concern for investors in Crocs, Inc. (NASDAQ: CROX). But with the stock currently at stratospheric levels (CROX hit an all-time high today at $91.18, and is only going higher in after-hours trading) and many other safety concerns, from the dismemberment-by-escalator stories (I know, I know, I'm exaggerating!) to simple day-to-day trials of too much bark dust in kids' feet, the tide could be turned quickly. One too many cases of banned or boycotted Crocs and investors could see some of their amazing profits turn to ... so much bark dust.

Do you love or hate Crocs? See our gallery for more.

MOST NOTEWORTHY: MGM Mirage (MGM), USA Truck, Inc (USAK), Knightsbridge Tankers Ltd (VLCCF), Monolithic Power Systems, Inc (MPWR) and Stanley, Inc (SXE) topped out today's noteworthy upgrade list:

• Prudential upgraded shares of MGM Mirage (NYSE: MGM) to Overweight from Neutral on valuation, as the firm believes the recent weakness presents a buying opportunity.

• USA Truck Inc (NASDAQ: USAK) was raised to Equal Weight from Underweight at Stephens based on valuation.

• Jefferies upgraded shares of Knightsbridge Tankers Ltd (NASDAQ: VLCCF) to Hold from Underperform to reflect the company's five vessels now operating on long-term time charter contracts and its recent entry into the dry bulk shipping sector.

• Monolithic Power (NASDAQ: MPWR) was upgraded to Buy from Hold at Deutsche Bank following its patent win case against O2Micro International Ltd (OIIM).

• Wachovia upgraded Stanley Inc (NYSE: SXE) to Outperform from Market Perform based on its strong Q4 report and guidance...

OTHER UPGRADES:

• Cognos Inc (NASDAQ: COGN) was upgraded to Outperform from Sector Perform at Pacific Crest.

• Riverbed Technology, Inc (NASDAQ: RVBD) was raised to Overweight from Market Weight at Thomas Weisel.

• Stifel upgraded Priceline.com Inc (NASDAQ: PCLN) to Buy from Hold.

• Barrington raised X-Rite, Inc (NASDAQ: XRIT) To Outperform from Market Perform.

• Morgan Stanley raised Principal Financial Group Inc (NYSE: PFG) to Equal Weight from Underweight.

Analyst summaries provided by TheFlyOnTheWall.com (subscription required).