As President Obama appeals for better relations with Iran, unnamed U.S. officials are pointing fingers at Iranian hackers for spying on U.S. Navy computers.

U.S. officials are saying that Iranian government or state-sponsored hackers penetrated an unclassified U.S. Navy computer network used for email and the “service’s internal intranet,” the Navy Marine Corps Internet, the Wall Street Journal reports.

The most recent incident occurred last week, said the officials. No sensitive information was stolen, nor were the email accounts of top officials compromised. Hackers used an unsophisticated means to penetrate the network, revealing a weakness in the Navy’s system, the officials said.

“The allegations would mark one of the most serious infiltrations of U.S. government computer systems by Iran,” the Wall Street Journal reports. “Previously, Iranian-backed infiltration and surveillance efforts have targeted U.S. banks and computer networks running energy companies, current and former U.S. officials have said.”

Follow Josh on Twitter and Facebook