Every quarter, many money managers have to disclose what they've bought and sold, via "13F" filings. Their latest moves can shine a bright light on smart stock picks.

Today, let's look at Viking Global Investors, founded in 1999 by Andreas Halvorsen and David Ott, who had previously worked together at Julian Robertson's respected Tiger Management firm. Viking is known as a long-short global equity fund, meaning that it aims to maintain long positions in companies on which it's bullish, and short positions in those where it's bearish.

The company's reportable stock portfolio totaled $14.2 billion in value as of September 30, 2012.

Interesting developments
So what does Viking's latest quarterly 13F filing tell us? Here are a few interesting details:

The biggest new holdings are Williams Co. (NYSE:WMB) and Danaher (NYSE:DHR). Other new holdings of interest include ARIAD Pharmaceuticals (NASDAQ: ARIA) and Hartford Financial Services (NYSE:HIG). ARIAD bulls are hopeful about its leukemia drug ponatinib getting FDA approval. Less exciting is the rejection that its bone-tumor drug ridaforolimus received in Europe. All isn't lost for that formula, though, as it might still prove effective against other cancers. The company's recent quarterly results were mixed, with cash burn a concern.

Hartford Financial, meanwhile, has struggled in this low-interest rate environment. With variable annuity sales down recently, Hartford has been focusing more on property-casualty insurance, while trying to buy out some of its variable annuity contracts, as well.

Among holdings in which Viking Global increased its stake was American International Group (NYSE:AIG). The company ran into serious trouble in the recent credit crisis, to say the least, but it's been turning itself around, and its life insurance and property and casualty insurance businesses have been doing well. To some, it seems quite attractively priced lately.

Viking Global reduced its stake in lots of companies, including priceline.com (NASDAQ:BKNG). The company has been growing briskly internationally, thanks, in part, to some savvy acquisitions, and its domestic and Asian growth has been offsetting sluggishness in Europe. The company's earnings and revenue have been experiencing steep -- and accelerating -- growth rates, 100% and 41%, respectively, over the past year. Some think the stock has risen too quickly lately, while others see it as fetching, with more room to run – partly due to its recent purchase of Kayak (NASDAQ: KYAK).

Finally, Viking's biggest closed positions included Pfizer (NYSE:PFE) and Host Hotels & Resorts (NASDAQ:HST). Other closed positions of interest include Skyworks Solutions (NASDAQ:SWKS), which makes components for smartphones. The fact that it's inside iPhones has many very excited, but some worry that it's rather dependent on one key customer. Others point out that it actually serves many other markets, such as the automotive, medical, avionics, and military ones, and other manufacturers, too. It was recently downgraded by the folks at Zacks, due to shrinking margins and lowered guidance.

We should never blindly copy any investor's moves, no matter how talented the investor. But it can be useful to keep an eye on what smart folks are doing. Therefore, 13-F forms can be great places to find intriguing candidates for our portfolios.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.