A few thousand Vanguard investment customers thought they had made some extra bucks on Monday.
But it turned out to be a software glitch: Vanguard account holders who were checking their balances on Apple iPhones, iPads, and Apple Watches - in short, anyone using an operating system on an Apple device - briefly experienced inflated values.
"A few thousand out of our 20 million clients" were affected, according to Vanguard spokeswoman Katie Hirt.
Hirt said 16 percent of customers who visit the company's website Vanguard.com do so through an Apple device and application. Of those, 11 percent clicked on the faulty app, she said.
The problem was related to Vanguard, not Apple, the Malvern-based company said.
It was fixed by Monday night, the day the inflated balances showed up.
"It's a big deal because it's a mistake. There should be no difference in numbers," said Dan Wiener, editor of the Independent Adviser for Vanguard Investors.
Vanguard Group has grown to $3.4 trillion in investor assets and dominates low-cost index mutual funds, the do-it-yourself investments.