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 Imperva Inc (NASDAQ:IMPV) fell nearly 44% Thursday after the company announced preliminary first-quarter results.

So what: Imperva isn't set to report full financial results until May 1, but based on preliminary information, the company expects quarterly revenue in the range of $31 million to $31.5 million, or well below previous guidance of sales in the range of $36 million to $37 million. This should translate to an adjusted net loss per share between $0.44 and $0.40, compared to Imperva's previous guidance for a net loss per share between $0.37 and $0.33.

Analysts, on average, were modeling a first quarter loss of $0.35 per share on sales of $36.69 million.

Now what: Management blamed extended sales cycles on deals of more than $100,000 for the revenue shortfall, the result of "intensifying competition for large orders" that led to "additional review and approval cycles as well as sales execution challenges in the U.S."

Of course, the prevailing worry among investors is that these sales might not just be delayed, but ultimately lost to that competition. As a result, and despite today's enormous plunge, I think investors would be wise to avoid opening new positions until we receive more clarity on Imperva's forward guidance on May 1.