"For a short period of time, new users who signed up were assigned erroneously to the same email account," said Lisa Pollock, senior producer for Yahoo Mail. "When they signed up for a Yahoo email account, we had multiple IDs that were assigned to a single Yahoo.com address."
New members, possibly numbering "in the hundreds," were assigned to two email addresses that Yahoo knows of before the problem was straightened out, Pollock said. She added that people with existing accounts were not affected.
"In the context of all the users who could have signed up in that period, it's a tiny number," Pollock said. "But it's an issue, so we fixed it."