If any group of investors pays attention to Vanguard's website, it's the Bogleheads.

So when the Vanguard website wasn't available over the weekend, between Saturday morning and Sunday morning, reading "Upgrade in Progress,"  the Vanguard devotees took their displeasure online.

Where? At the Bogleheads website, naturally. The Bogleheads are a collection of penny-pinching, self-educated investors who love Vanguard's philosophy of low-cost indexing and investing, made famous by founder John Bogle. They share education, information and ideas — all for free, of course — at Bogleheads.org.

"Wow, let's spend the entire weekend (NOT) trying to figure out what the upgrades might be, deliberating if it's an upgrade if Fidelity/Schwab already have it, then when it comes up complaining about how it's different and we don't like change," wrote Rick Boglehead on the website.

"I just logged on and am not seeing any balances," wrote another. "Also received a message that my computer was not recognized when I tried to log on. It is the same computer that I have used for 5+ years. Luckily I could answer my security question — but still no balances. I find it highly unusual that Vanguard does not provide a time frame as to when they expect to complete their website maintenance."

Others were pleased to hear that the Malvern-based investment giant was coming through with their promise to upgrade technology.

"I'd guess the downtime is due to heavy database changes to schema or architecture, and the need to verify data consistency according to some strict industry regulations," wrote Vanguard customer Richann.

"All is well," wrote another, self-described "IT guy for 35yrs, many upgrades in my life. Backup copies, offsite copies, ample test time. Relax everyone."

Last month, when the Dow and the S&P 500 index both dropped more than 3 percent, Vanguard's website failed, blaming a "network connectivity issue," according to a tweet that Vanguard repeatedly sent to clients who tweeted about their inability to log in or trade.

Vanguard has said it is investing "heavily" in technology. The firm manages more than $5 trillion in assets globally.

The goals, outgoing chairman Bill McNabb has said, include making life easier and more convenient for clients and providing them with an enhanced experience.

McNabb didn't put a number on technology spending. Tim Buckley, Vanguard's chief executive, said nothing about service issues that the company's clients have experienced.

Fidelity Investments has been less shy about estimating spending. Barron's recently reported that Fidelity is spending $2.5 billion a year on technology.

Vanguard, for its part, issued a statement Monday saying: "Over the weekend, Vanguard completed a long-scheduled upgrade of our systems — part of our broader, multi-year reinvestment efforts to improve our client service and experience. As a security precaution and following industry best practices, we cannot disclose the details of the upgrade."