McAfee Inc.'s (MFE) third-quarter profit fell 25% on higher costs, which affected margins, as the antivirus-software maker posted higher worldwide revenue.

The company also projected fourth-quarter earnings of 61 cents to 65 cents a share on revenue of $505 million to $525 million. Analysts polled by Thomson Reuters expected 63 cents and $507 million, respectively.

Shares fell 2.9% to $42.60 in after-hours trading as the quarter's results were also merely in line with expectations. At the close, the stock was up 27% this year.

McAfee has been buying up smaller companies recently, including its recent acquisition of MX Logic Inc., a provider of cloud-based e-mail and Web security. McAfee's product portfolio and business deals have mostly helped it fend off the worst of the gloom of 2009, although it isn't immune to the information-technology spending slowdown.

McAfee posted earnings of $36.8 million, or 23 cents a share, down from $48.8 million, or 31 cents a share, a year earlier. Excluding stock-compensation and acquisition costs, earnings rose to 62 cents from 53 cents.

Revenue jumped 18% to $485.3 million amid a 25% increase in North America. International revenue grew 11%.

In July, the company projected earnings of 58 cents to 62 cents on revenue of $475 million to $495 million.

Gross margin fell to 73.9% from 76%.

-By John Kell, Dow Jones Newswires; 212-416-2480; john.kell@dowjones.com