 "Apple users under first Mac ransomware attack")
Apple's shares were down 7% at $97.09 after its first revenue decline in 13 years, while Twitter slumped 16% to $14.91 after its revenue missed expectations.
Investors are awaiting a Fed decision on rates at 2 p.m. ET (1800 GMT). No change in rates is expected but the Fed may signal its intention to tighten policy this year.
Read more from our special coverage on "APPLE"
Economists polled by Reuters expect two increases this year but futures prices show traders do not expect rates to rise until late 2016, according to CME Group's FedWatch.
"I don't think the Fed is going to raise rates today but they are starting to lean towards the possibility of a hike and are going to buy themselves some insurance by saying that June is more possible than a lot of people ... think," said Brad McMillan, chief investment officer for Commonwealth Financial in Waltham, Massachusetts.
The Fed next meets on June 14-15. While the labor market continues to gain strength, inflation remains below the central bank's 2% target and mixed economic data could cloud the path to future rate hikes.
At 9:43 a.m. ET, the Dow Jones industrial average was down 23.62 points, or 0.13%, at 17,966.7, the S&P 500 was down 1.25 points, or 0.06%, at 2,090.45 and the Nasdaq Composite was down 28.24 points, or 0.58%, at 4,860.04.
Six of the 10 major S&P sectors were higher, with the energy index's 1.13% rise leading the advancers.
Oil hit its highest level this year on Wednesday, driven by a falling dollar and evidence of declining U.S. supply, putting the price on course for its strongest monthly performance since last April.
Disappointing earnings have slowed down a recent rally but the S&P continues to hold near the record high it set almost a year ago. The index has rallied 15% since February.
First-quarter earnings from S&P 500 components are expected to have fallen 7.1% from a year earlier, according to Thomson Reuters I/B/E/S. Of the 166 companies that have reported, 59% reported revenue above analyst expectations, just short of the average 60% since 2002.
Facebook and PayPal are scheduled to report results after the close of market.
DreamWorks Animation rose 15% to $31.20 after the Wall Street Journal reported Comcast was in talks to buy the Hollywood studio owner. Comcast was up 2.8%.
Ebay was up 5.6% at $25.88 after raising its full-year revenue forecast, while Boeing fell 0.9% to $132 after a drop in quarterly profit.
Chipotle was down 4.3% at $426 after a bigger-than-expected drop in quarterly comparable sales prompted a spate of price target cuts.
Advancing issues outnumbered decliners on the NYSE by 1,685 to 983. On the Nasdaq, 1,160 issues rose and 1,121 fell.
The S&P 500 index showed 12 new 52-week highs and 2 new lows, while the Nasdaq recorded 30 new highs and 8 new lows.
