Key muni market website reportedly hobbled by ransomware attack

[Selective focus of dollar notes and red tag written with MUNICIPAL BONDS on white wooden background.]
Mohamad Faizal Bin Ramli

A platform that's key for the $4.3T municipal bond market has been incapacitated by a ransomware attack, according to a media report on Wednesday.

MuniOS.com, operated by Ann Arbor, Michigan-based ImageMaster, is used by thousands of borrowers to distribute their offering documents. The service has been out of service for several days, due to the attack, Bloomberg News reported [https://www.bloomberg.com/news/articles/2025-10-15/ransomware-attack-ensnares-4-3-trillion-muni-market-s-key-site?srnd=homepage-americas], citing people familiar with the matter.

The service is popular with investors and analysts to access information about transactions before they're sold. In 2017, Bloomberg reported that MuniOS.com had a market share exceeding 70%.

On Tuesday, the Municipal Securities Rulemaking Board, a market self-regulatory organization, issued a notice [https://www.msrb.org/sites/default/files/2025-10/MSRB-Notice-2025-06.pdf] informing issuers that they can use its EMMA website to post preliminary official statements and other market information. However, it didn't mention the MuniOs.com outage.

Relevant ETFs: iShares National Muni ETF (NYSEARCA:MUB [https://seekingalpha.com/symbol/MUB]), VanEck HIgh Yield Muni ETF (BATS:HYD [https://seekingalpha.com/symbol/HYD]), VanEck Intermediate Muni ETF (BATS:ITM [https://seekingalpha.com/symbol/ITM]).

MORE ON ISHARES NATIONAL MUNI BOND ETF, VANECK HIGH YIELD MUNI ETF, ETC.

* MUB: A Low-Cost, Investment-Grade Municipal Bond Fund [https://seekingalpha.com/article/4827552-mub-low-cost-investment-grade-municipal-bond-fund]
* MUB Vs. VTEB: Do Not Miss VTEB's Buy Window Before Interest Rate Cuts [https://seekingalpha.com/article/4819901-mub-vs-vteb-do-not-miss-vteb-buy-window-before-interest-rate-cuts]
* HYD: High Yield Munis Present A Clear Contrarian Play (Rating Upgrade) [https://seekingalpha.com/article/4808559-hyd-etf-high-yield-munis-present-clear-contrarian-play-upgrade-strong-buy]
* Treasury yields extend slide after holiday; 10-year nears 4% [https://seekingalpha.com/news/4503774-treasury-yields-extend-slide-after-holiday-10-year-nears-4]
* If Washington and Beijing don’t blink, markets could face a hard fall, Mike Wilson says [https://seekingalpha.com/news/4503607-if-washington-and-beijing-don-t-blink-markets-could-face-a-hard-fall-mike-wilson-says]