Synacor Inc., a provider of technology that verifies pay TV subscribers and allows them to access online streams of programming, on Wednesday reported a sharp rise in second-quarter net income and revenue, as more people used its "TV Everywhere" services and it served up more ads.

But it issued guidance for its third-quarter and full-year revenue that fell short of forecasts and shares plunged 18 percent in afterhours trading.

Net income in the three months to June 30 was $1.2 million, or 4 cents per share, up from $51,000, or 3 cents a share, a year earlier. The prior year's net income number excludes $541 million of undistributed earnings allocated to preferred stockholders.

The net income results for the latest quarter matched estimates by analysts polled by FactSet.

Revenue rose 58 percent to $30.8 million, a tad higher than the $30.7 million expected by analysts.

The average number of people who visited its customers' websites rose to 20 million a month from 13.9 million a month during the prior-year quarter. The number of advertising impressions served during the quarter rose to 10.3 billion from 6 billion.

For the third quarter, however, Synacor projected revenue of $28 million to $28.5 million, below the $30.6 million expected by analysts.

It also said revenue for the full year is expected to be on the lower end of its previous guidance of $123 million to $126 million. Analysts had expected full-year revenue of $125.3 million.

Synacor's stock tumbled $2.26 to $10.60 in extended trading following the release of the earnings report.