The amount of malicious adware more than doubled last year as cybercriminals adjust their strategy in the wake of better security elsewhere, according to a new malware report from G Data Software.
In the second half of 2014, adware accounted for 31.4 percent of all new malware signatures, up from 14.1 percent during the first half of the year.
This total includes adware products that infect existing ads to cause malicious downloads, intrusive popup ads, and malware that injects new ads into websites.
Adware is now the second most-common malware category, having passed downloaders for the first time last year. It is quickly catching up to Trojans, which are still, by a slim margin, in first place.
Adware was in fifth place at the end of 2013, and in seventh place at the end of 2012.
"The bad guys have figured out that this is an opportunity," said G Data security evangelist Andy Hayter. "But also, they're finding that the opportunity to gather money through other malware channels is getting tighter. For example, there's mitigation in place that has made it more difficult to use banking Trojans."
The number of targeted banking customers in the US fell by 12 percent, the report said, while the number of averted banking Trojan attacks rose by 45 percent.
"Improved security measures by banks are making it more and more difficult for online bank robbers to get money from bank customers," said Ralf Benzmüller, head of G DATA SecurityLabs.
For example, banks are increasingly rolling out two-factor authentication, which makes it more difficult for criminals to empty bank accounts even when they have login credentials. Banks are also using more analytics behind the scenes -- for example, automatically blocking unusual or large transfers to new destinations.
Hayter also pointed out that some of the major criminals being the banking Trojans have gotten caught.
"You're seeing a lot more focus on this from law enforcement to shut this down," he said.
As a result, banking malware is simultaneously becoming riskier and less profitable for the criminals.
Annoying pop-up ads don't garner the same amount of attention, he said. In fact, many users might just close the ads without realizing that their computers were infected.
"This is a target that offers better opportunity to make money," he said. Once browser vendors step up their security, however, the criminals are likely to move on to something else, he added.
However, the absolute numbers for total Trojan and downloader malware strains have each almost doubled.
G Data recorded a total of nearly 6 million new malware variants last year, up from 3.4 million in 2013.
Hayter expects the growth in malware to continue because of new malware tool kits that make it easy to create new strains.
In addition, he said, the toolkits themselves have been hacked into and pirated, making it easy for other criminals to create new toolkits