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 AVG Technologies (NASDAQOTH:AVGTF) plunged today by as much as 12% after the CEO resigned.

So what: The news comes just weeks after AVG jumped 14% on better-than-expected earnings and guidance. J.R. Smith said he is stepping down but will stay on as CEO until a successor is found. COO John Giamatteo will handle daily operations until then.

Now what: Smith said he felt it was the right time to hand over the reins to new leadership. He had led AVG for the past six years. The outgoing executive will become a member of AVG's Supervisory Board, and AVG has tapped SPMB to search for a new CEO. Investors are caught off guard from the move, and that surprise is manifesting itself with today's sell-off.

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Fool contributor Evan Niu, CFA, has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. 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 has a disclosure policy.