LEESBURG, Virginia — A judge dismissed a felony spamming conviction that had been called one of the first of its kind, saying he found no “rational basis” for the verdict and wondering if jurors were confused by technical evidence.

Ruling Tuesday, Judge Thomas D. Horne also said jurors may have gotten “lost” when navigating Virginia’s new anti-spam law in the case of Jessica DeGroot. But Horne upheld the conviction of her brother, Jeremy Jaynes, who prosecutors said led the operation from his Raleigh, North Carolina, area home.

DeGroot, 28, and Jaynes, 30, were each convicted in November for using false Internet addresses to send mass e-mail ads through an AOL server in Loudoun. The jury recommended that Jaynes spend nine years in prison and that DeGroot pay $7,500 in fines.

Prosecutors had called the felony convictions the nation’s first for spamming.

They said the siblings and a third defendant, Richard Rutkowski, sent more than 10,000 spam e-mails over three days in July 2003. Rutkowski was acquitted.

Jaynes’ attorney, David A. Oblon, had argued that the spamming was not conducted in Virginia and that there was no evidence that e-mails were unsolicited. Oblon said he would appeal.