Yesterday Brian Halligan and Dharmesh Shah, the co-founders of HubSpot, the ballyhooed marketing-software company whose market cap exceeds $1 billion, responded to a new book that is highly critical of the company's culture and product. 

The book, "Disrupted," came out April 5. The author is Dan Lyons, a former Newsweek tech editor who spent 20 months at the Cambridge, Mass.-based HubSpot in 2013 and 2014. He's since gained fame as a writer for the HBO Comedy "Silicon Valley."

To be sure, HubSpot's response is measured and timely. Though it appears one full week after the book's release, that timing makes sense given that the co-founders had to actually read and digest the book. But their response--while providing some direct, compelling counterpoints to Lyons' observations and opinions--is also elusive about several matters that "Disrupted" has brought to light.

So what did Lyons write about HubSpot, and how well did HubSpot respond? Here's the fast version:

Lyons described HubSpot's culture as ageist, cult-like, and sometimes cruel. The book makes it plain that he didn't enjoy working there, and felt like an outcast as a 52-year-old among a large cast of twenty-somethings. Lyons points out that fired employees are euphemistically referred to as employees who have "graduated."

In their response to "Disrupted" on LinkedIn, the co-founders address the critique head on. They note that HubSpot ranked fourth in Glassdoor's most recent rankings of best places to work, and that Glassdoor's top 10 includes Facebook, Google, and LinkedIn. "Though we're disappointed that Dan's experience at HubSpot was in such stark contrast to that of most of our employees, he is, of course, entitled to his opinion," they write. 

As for that "graduation" euphemism--the founders fess up to it, saying they used the term not as an insult, but because the Hubspot alumni group is strong. "Alumni get together and talk about their careers, the startup ideas they're working on and generally just hang out and help each other out," they write. "Since we call this group 'alumni,' we thought that the term 'graduation' made sense to use. A while back, we realized that it was a mistake. It was disrespectful and misleading--not our intention at all. Lesson learned and change already made. We're sorry."

In the book, Lyons asserts that HubSpot's business model amounts to glorified spamming. He's especially critical of the company's inbound-marketing methodologies, wherein Hubspot customers use blogs, email, and other content to lure prospective customers to their web sites.

Halligan and Shah reply that inbound marketing is "the exact opposite of spam:"

Our more than 18,000 customers can vouch for that. It is based on a very simple idea: As people have increasing power and control over the 'inputs' into their lives, it becomes harder and harder to interrupt them with irrelevant, non-useful things. So, the only way to reach them is by pulling them in. Don't try to invade their world, but instead, invite them into yours. And the way to do that is to be helpful, say useful things and be respectful of their time. 

Indeed, it's hard to argue with HubSpot's 18,000 paying customers or $180 million in 2015 revenue. While anyone can relate to how annoying it is to receive an unsolicited email from a company, HubSpot's growth makes a compelling case that its approach helps companies generate sales--even if it's an approach that, under some circumstances, invades email inboxes with unwanted semi-solicitations. 

So where does HubSpot's response fall short?

Lyons devotes a lot of ink to insulting the quality of HubSpot's software. He also compares HubSpot's young employees to brainwashed corporate zombies. In their response, the co-founders ignored these slings and arrows. 

What's more, the company continues to remain mum about what happened last summer, when federal law enforcement officials opened a criminal investigation into alleged attempts by former HubSpot executives to obtain a prepublication draft of "Disrupted."

Though federal investigators dropped the case without pressing any charges, the incident caused HubSpot to fire then-CMO Mike Volpe, who'd worked as Lyons' boss. The incident also led to the resignation of vice president Joe Chernov and a pay cut for Halligan, "who knew about Volpe's actions but failed to bring the ethical violation to the board's attention in a timely fashion," reports the Boston Globe.

Granted: It's seldom easy or advisable to comment on legal matters. And you can't blame HubSpot for wanting to put the scandal behind it. But in their response to "Disrupted," the co-founders didn't even give lip service to the fact that the scandal happened. The closest they come is in their postscript, which reads: 

p.s. We know that there are many questions the broader community has about the book. Though we can't answer all of them, we're going to attempt to address some of them here.

When it comes to their culture and their business model, the co-founders address those questions. You come away feeling as if you understand their side of the story. When it comes to why their former co-workers tried to obtain a prepublication version of "Disrupted," the co-founders ignore the topic. And it leaves you scratching your head.