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 Chinese mobile and online portal SINA (Nasdaq: SINA) lost signal today, falling as much as 16.1% on heavy trading.

So what: This stock is caught in a three-way perfect storm today: Some analysts worry about a slowing Chinese economy, others see drastic downside changes resulting from new regulation of variable-interest entities, and still others panic over the Department of Justice, SEC, and FBI investigating suspected Chinese accounting frauds.

Now what: There might be something to two of those big-picture worries, but I wouldn't accuse SINA of fraud. The SEC is more worried about "now you see them, now you don't" gadflies hoping to grab a quick buck from an American IPO and then flame out in a blaze of founder-enriching infamy. SINA has a long operating and market history, including a seven-year stint on our Stock Advisor scorecard, and doesn't fit that profile at all.

Interested in more information about SINA? Add it to My Watchlist.

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.