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 Internet service and mobile security specialist Qihoo 360 Technology (NYSE: QIHU) look anything but secure today, falling as much as 19.1% on more than double the average trading volume.

So what: The newswires from Qihoo are quiet as a mouse, but there's plenty of large-scale options trading to go along with the sudden stock move. A truckload of in-the-money puts expiring today have changed hands while July puts with low strike prices and calls with high ones traded even more briskly.

Now what: I think we're looking at some deliberate market manipulation here. Traders large and small jockey for position, attempting to squeeze profits out of their options just as they expire on today's quadruple witching hour. There's similar action going down around industrial manufacturer Jinpan International (NYSE: JST). What makes Qihoo different is that the stock is heavily traded anyway, making it that much harder to bend to a trader's will. There must be large fortunes at play here.

Interested in more info on Qihoo 360 Technology? Add it to your watchlist.

Fool contributor Anders Bylund holds no position in any of the companies discussed here. The Motley Fool owns shares of Jinpan International. Motley Fool newsletter services have recommended buying shares of Jinpan International. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool is investors writing for investors.