Updated from 4:46 p.m. EDT

Antivirus software maker

Symantec

(SYMC) - Get Report

said Monday that it has discovered a $20 million error in its calculation of deferred revenue.

The news pushed shares of Symantec down $1.37 a share, or 3%, to $44.20 in recent after-hours trading; the stock closed the regular session at $44.57, a gain of 6 cents.

To correct this error, the income statement will reflect a $20 million reduction in revenue during the three-month period ended July 2, 2004, with a corresponding $20 million increase in deferred revenue in the balance sheet as of July 2, 2004, the company said in a press release.

Net earnings per share for the July quarter will be reduced to 33 cents, 4 cents below what was previously announced, according to generally accepted accounting principles. Non-GAAP earnings will be cut by 3 cents to 36 cents per share.

Guidance for the full year will not change, but the company now expects revenue of $588 million in the October quarter, an increase of $8 million from prior guidance. Pro forma EPS will likely be 35 cents, an increase of a penny.

The $20 million figure is actually an accumulation of the error over nine quarters, beginning with the first quarter of fiscal 2003 and continuing through the first quarter of fiscal 2005, a spokeswoman for the company said.

The error occurred because an accounting tool built by the company to help calculate deferred revenue did not recognize the fluctuating value of the dollar, she added.