There were 28 critical bulletins in 2014, down from 42 in 2013, while the average number of common vulnerability exposures stayed the same.
There are two possible explanations for this, said Craig Young, a Tripwire security researcher.
"Either Microsoft is trying to make it a little easier for administrators," he said, "Or they're playing with the numbers a little bit to give the impression that they're improving security a little more than they have been."
Not that they haven't been improving security, he added.
"With the newer Microsoft software, we're generally seeing better protections," he said. "The features built into the defensive systems have gotten better, and the vulnerabilities have gotten more complex to exploit."
However, the discovered vulnerabilities continue to be high impact, said Mike Lloyd, CTO at Sunnyvale, Calif.-based RedSeal, Inc.
"Almost half of the announced vulnerabilities allow a remote attacker to execute unwanted code," he said.
According to the Tripwire report, which sorted the patches by their security impact, the single largest category last year was "remote code execution," with "elevation of privilege" being the next largest group.
These are also the two most dangerous types of vulnerabilities, said Jerry Irvine, CIO at Chicago-based security firm Prescient Solutions.
"Having a combination of those two risks out there really causes the types of breaches and loss of data that is occurring today," he said.
Irvine added that it's particularly worrisome that new vulnerabilities are constantly being discovered that have been in place for a long time.
"The Jasbug has been out there for 15 years and is now just being fixed," he said.
If somebody knew about it, they've been able to exploit it for a while, he said.
However, some of the increase in vulnerabilities could also be due to the fact that existing vulnerabilities are being fixed, he said. Hackers have to keep finding new ones -- often, by tweaking previously discovered vulnerabilities.
"The good news is that Microsoft is fixing stuff," said Gary McGraw, CTO at Dulles, Vir.-based security firm Cigital, Inc. And if the patches are coming out on a predictable schedule, that's even better, he said, since some administrators want to do testing before pushing the patches out to the enterprise.
The actual numbers of vulnerabilities doesn't matter as much, he said. "What really matters is fixing them."
Tripwire also broke out the numbers for Internet Explorer. Here, the number of bulletins has been growing slowly but steadily over the past four years.
"I'd like to see the data without Internet Explorer," said Russ Ernst, director of product management at Scottsdale, Ariz.-based Lumension Security, Inc.
For example, in this week's Patch Tuesday, there were 56 vulnerabilities addressed in the nine bulletins -- but 41 of those were part of the single Internet Explorer cumulative update.
"This is analogous, in my mind, to when economic data is presented," Ernst said. "There's a general increase or decrease in GDP, but then most economists take a look at the data excluding food and energy prices which are highly dynamic. If we remove Internet Explorer from the data, I bet that number is a lot more stable."