A new report by security vendor ESET holds mixed news for enterprises running on Microsoft technology.

Microsoft last year fixed nearly twice as many vulnerabilities across all its products than it did in 2013. But a vast majority of the reported flaws were in Microsoft's Internet Explorer browser, suggesting that the company's efforts to secure its core Windows operating system environment itself may finally be working.

"Windows overall had a more secure year than in 2013," says Aryeh Goretsky, security researcher at ESET. There were relatively fewer zero-day flaws and other major vulnerabilities that Microsoft had to patch in Win 32, Office, .Net, and other major Windows components compared to a year ago.

"A lot of the attacks we saw were fairly routine pieces of code doing routine kinds of attacks," Goretsky says. "We didn't see any particularly stealthy or military grade Stuxnet-like malware," targeting Windows in all 2014, Goretsky says. "What we saw were just regular malware families that have been around for several years being updated as new vulnerabilities become available," through the year.

But enterprises have no reason to drop their guard, cautions Goretsky. Even as discovered vulnerabilities and attacks against Windows fell in 2014, the number of flaws that Microsoft had to patch in Internet Explorer soared to around 240, or double the number the company had to fix in 2014.

Most of the IE flaws reported last year enabled remote code execution meaning they could be used to implement drive-by download attacks. At least five of the reported IE vulnerabilities were exploited in the wild before Microsoft had a chance to issue a security patch, the ESET report showed.

Goretsky says the number of vulnerabilities reported in IE last year suggests that attackers are turning their attention to the browser because they think it offers an easier way into a network than attacks against core Windows components.

"Hackers are interested in making money. If something becomes more secure they start looking for another way into your systems," he says. The typical tendency is to go after the network infrastructure, or to look for vulnerabilities in third-party software or tool chains.

"It's like a thief trying to rattle all the windows in the house," if they can't get in via the front door, he says.

Richard Stiennon, chief research analyst at IT-Harvest says the increased attention on IE makes sense. "It sounds reasonable. I have also heard that Adobe hacks have become more prevalent than Microsoft OS hacks," for the same reason, he said in emailed comments.

John Pescatore, director of emerging security threats at SANS Institute, concurs that the core Windows operating system environment has gotten more secure. "But I think attacks against browsers in general have gone up versus attacks against the operating system," he said in an email. Considering that IE has nearly three times the market share of Chrome when all versions are combined, the trend poses a problem from enterprises, he said.

The ESET report pointed to several techniques that Microsoft has employed over the years to bolster Windows security. Among them is its Data Execution Prevention (DEP) feature for stopping malware code from running on a system and Microsoft's Address Space Layout Randomization (ASLR), which the company first introduce with its Vista launch. A similar Enhanced Protected Mode (EPM) mode introduced with IE10 could make the browser harder to crack by offering a full sandbox for the browser, the ESET report said.

ESET's report on Windows vulnerabilities comes the same week that Microsoft in a surprise move decided to stop issuing its usual free alerts for Patch Tuesday. The Advance Notification Service basically detail the number of security patches the company will release the following week and are designed to give enterprises some time to prepare for them.

In a blog post, Chris Betz, senior director for the Microsoft Security Response Center (MSRC) described the move as a response to evolving technology environments and customer needs. Going forward, Microsoft will only make ANS available to Microsoft's paying Premier customer and organization's currently involved in its security programs. The notifications will no longer be available for free, Betz said.

"While some customers still rely on ANS, the vast majority wait for Update Tuesday, or take no action, allowing updates to occur automatically," Betz wrote.