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.