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 network gear maker F5 Networks (FFIV 0.38%) plunged 12% today after its quarterly results and outlook missed Wall Street expectations.

So what: F5's wide fourth-quarter miss -- adjusted EPS of $1.12 versus the consensus of $1.19 -- and downbeat guidance for the current quarter reinforce concerns over its vulnerability to the soft global economy. Like rival network equipment maker Juniper Networks (NYSE: JNPR), F5 continues to be seriously hurt by weak spending from big telecom customers, giving investors little hope for a near-term turnaround.

Now what: Management now sees first-quarter adjusted EPS of $1.14-$1.16 on revenue of $363 million-$370 million, well below the consensus of $1.20 and $373.5 million, respectively. "While we are excited about these new products and their potential to drive revenue growth, current macroeconomic conditions and our expectation of normal Q1 seasonality have tempered our outlook for the near term," cautioned CEO John McAdam. Of course, with the stock now off about 40% from its 52-week highs and trading at a forward P/E of 15, now might be a good time to buy into F5's still-attractive long-term prospects.

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