MARKET SNAPSHOT: S&P 500, Nasdaq Suffer Worst Weekly Loss Since May 2012

By Anora Mahmudova and Carla Mozee, MarketWatch

NEW YORK (MarketWatch) -- After a sharp selloff in U.S. stocks on Friday the main benchmarks recorded their deepest weekly declines in more than two years.

The tech-heavy Nasdaq Composite (RIXF) dropped 102 points, or 2.3%, to 4,276.24 and suffered its worst weekly decline since May 2012. The index undercut a key support level, prompting fears of further declines.

The S&P 500 (SPX) fell 22 points, or 1.1%, to 1,906.13, losing 3.1% over the week, its biggest weekly drop since May 2012. The benchmark index is a hair's breadth away from undercutting its key support level.

The Dow Jones Industrial Average (DJI) dropped 115 points, or 0.7%, to 16,544.10, and lost 2.7% over the week. The blue-chip index turned negative for the year and also fell below its key support level.

The whiplash equity moves have been characterized by a spike in volatility (a measure of fear in the markets) on concerns about slowing global growth. The widely watched CBOE VIX (VIX) a gauge of current fear in the market, surged 45% over the week and is at highest level since February.

"Bad economic data is now being viewed as bad and the dovish signals from central banks are now being taken as a sign of weakness rather than a reason to ramp up equities," wrote Jonathan Sudaria, a dealer at Capital Spreads, in a Friday note that highlighted the rout in European stocks. The Stoxx Europe 600 was looking at its biggest weekly loss in more than a year, with Germany's economic ministry saying Friday the growth outlook for Europe's largest economy is dimming.

Data: The prices paid for imported goods fell 0.5% in September and declined for the third straight month, another sign that U.S. inflationary pressures remain muted. The main reason: falling worldwide oil prices.

Stocks to watch: Biggest losses came from the technology sector. Internet stocks were hit hardest, with the Global X Social Media Index ETF (SOCL) down 3.1%. Twitter, Inc (TWTR) fell 8.8%, while Facebook, Inc (FB) lost 3.9%.

Tesla Motors Inc. (TSLA) late Thursday unveiled its latest Model S car. But shares slid 7.8% .

Symantec Corp. (SYMC) shares slid 6.4%. The security-software maker late Thursday said it plans to split into two publicly traded companies.

Juniper Networks Inc. (JNPR) fell 9% after a late Thursday warning that fiscal third-quarter revenue and adjusted earnings are likely to be below its previous estimates.

Exact Sciences Corp. (EXAS) shares rallied 36% as the company's Cologuard test to detect colorectal cancer will be covered by Medicare.

Alpha Pro Tech Ltd. (APT) is up 53% and Lakeland Industries Inc. (LAKE) is up 11% following gains from Thursday amid rising Ebola outbreak concerns. Alpha Pro Tech's infection control unit makes face masks and eye shields, and Lakeland makes protective clothing for health care and first responders.

Other markets: Crude-oil futures ended modestly higher Friday, but notched weekly losses that were the steepest since January for New York-traded oil.

Gold futures (GCZ4)edged lower Friday, with a stronger U.S. dollar trumping a further wave of risk aversion as global equities declined, taking a cue from a sharp selloff in U.S. stocks a day earlier. The dollar (DXY) was slightly higher against its rivals after Thursday's fall to a three-week low. In Asia, Hong Kong's Hang Seng Index and Tokyo's Nikkei Average fell 1.9% and 1.2%, respectively.

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