UPDATE 2-FireEye reneges on adjusted profit forecast, shares tumble

(Adds CFO comments, details on forecast; updates shares)

Nov 1 (Reuters) - Cybersecurity firm FireEye Inc said on Wednesday it was likely to post an adjusted loss for the fourth quarter, hurt by shorter contract lengths, disappointing investors who were promised an profit by the end of the year.

FireEye also gave a lower-than-expected billings forecast for the current quarter, indicating a weak revenue forecast and sending its shares tumbling more than 12 percent in trading after the bell.

The company, which is yet to report a profit since going public in 2013, expects its fourth-quarter bottom line, on an adjusted basis, to range between breakeven and a loss of 3 cents per share.

Analysts were expecting a loss of 1 cent per share, per Thomson Reuters I/B/E/S, despite the company saying it was targeting an adjusted profit by the end of 2017.

"We are taking a slightly more conservative view of the fourth quarter and narrowing the range," Chief Financial Officer Frank Verdecanna told analysts on a conference call.

"Because there are some larger committed subscription deals in our pipeline that look to have shorter contract lengths compared to what we were expecting when we iterated our annual guidance last quarter."

FireEye, which has investigated some of the biggest cyber attacks to date including the recent Equifax breach, typically offers one or three year subscriptions for its threat intelligence and support services, according to a regulatory filing in February.

FireEye forecasts fourth-quarter billings of $210 million to $230 million, below analysts' estimate of $237.4 million, according to research firm FactSet.

Billing includes revenue recognized plus the change in deferred revenue, which are an important indicator of the health and visibility of a company's business.

"It's been a bumpy road for FireEye over the past few years but it appears they are directionally heading in the right direction even though the bulls were hoping for more around the company's outlook," GBH Insights analyst Daniel Ives told Reuters.

The forecast was accompanied by stronger than expected results for the third quarter, with net loss attributable to shareholders narrowing to $72.9 million from $123.4 million.

Revenue rose 1.7 percent to $189.6 million.

Asked by Reuters about the impact of its response to the Equifax breach on product sales, CEO Kevin Mandia said: "I haven't seen any direct impact of that breach, other than, just additional awareness that the liabilities are significant."

FireEye's shares were down 12.34 percent at $14.35 in trading after the bell. (Editing by Patrick Graham and Savio D'Souza)