The Dow Jones Industrial Average (DJINDICES:^DJI) had shed more than 135 points as of 11:30 a.m. EDT Tuesday. A few tech stocks, however, were performing far worse than the market, as BlackBerry (NYSE:BB), FireEye (NASDAQ:FEYE), and Splunk (NASDAQ:SPLK) experienced notable sell-offs.

BlackBerry defends the Passport
Shares of Canadian handset company BlackBerry fell 5%, giving back nearly all of Monday's gain. BlackBerry has been an especially volatile stock in recent sessions, so its decline is not surprising.

Late on Monday, BlackBerry published an official blog post defending the design of its upcoming handset, the Passport. The BlackBerry Passport has received a notable level of attention in recent weeks due to its unconventional design: a large phone with a physical keyboard and square-shaped body.

BlackBerry argues that the Passport's square screen is ideal for productivity -- at 4.5-inches, it isn't as large as some of the larger Android handsets on the market, but the added width makes it easier for users to view documents.

The Passport alone won't dictate BlackBerry's future, but success here could help the company erase its losses. Last quarter, the company lost money, though less than analysts had anticipated. BlackBerry's management aims to hit breakeven by the end of the year.

Source: Wikimedia Commons.

FireEye continues to tumble
Shares of FireEye fell more than 8% late in the morning on Tuesday. FireEye shares had traded as high as $97 in March, but have been steadily declining in recent months. In just the last five sessions, FireEye stock has fallen roughly 16%.

Last week, Northland Securities initiated coverage on FireEye with a market perform rating and $37 price target. At the time, FireEye was trading above Northland's target, but is now well below that level. On Monday, Topeka Capital Markets defended the stock, reiterating its buy rating and $70 price objective, yet shares have continued to slide.

Investors may be skeptical of FireEye's valuation. The company is unprofitable and expects to remain so for the near future. Last quarter, FireEye posted a loss of $0.53 per share, and it said that it expects to lose more than $2 per share for the full fiscal year.

Splunk shares drop
Shares of Splunk fell more than 9%. Splunk is another tech stock that has come under heavy selling pressure in recent weeks: it is down about 15% in the last five sessions alone. Splunk's multimonth sell-off matches up well with FireEye's, but has not been nearly as severe. Splunk shares traded as high as $106 in Feburary, but have been more than cut in half since.

As with FireEye, it may be an issue of valuation. Despite having a market cap of more than $5.6 billion, Splunk is unprofitable: In its last quarter, it posted a generally accepted accounting principles loss of $0.43 per share and an adjusted loss of $0.04 per share.

To its credit, Splunk is seeing rapid revenue growth -- last quarter, revenue increased 50% from the prior year. But analysts have been cautious on the stock, with several recently reducing their price targets, and the company has seen some insider selling.