Symantec’s Blue Coat security firm recently announced some worrying trends regarding the use of SSL by malware. Specifically, the company discovered two major trends.

To start, the number of malware samples increased to more than 29,000 in November and December 2015, up from only 500 per month before October 2015. Additionally, the number of C&C servers using SSL increased to 200,000 per quarter in Q3 2016, up from 1,000 in Q1 2015.

Huge Spike in Malware Samples Using SSL

Blue Coat noted that it had discovered a significant jump in SSL deployment since the end of 2015. The firm studied data from the SSL Blacklist site, which monitors bad SSL certificates often used by cybercriminals.

Malware such as Dridex, Gozi, Tinba, Gootkit, CryptoWall, CryptoLocker, TeslaCrypt, URLZone and Shylock are known to use SSL to protect their operations from observation or detection.

Blue Coat explained that, starting in October 2015, the malware families known to utilize SSL saw a “rapid and dramatic surge in distribution and usage.” The firm posited that the spike, which coincided with the holiday season, may have been due to the launch of several large-scale cybercrime campaigns with infrastructure based on those malware families.

The trend, according to Blue Coat, exemplifies the widespread use of SSL/TLS as an obfuscation technique, “making the threat even more relevant than ever.”

Cybercriminals Get Proactive

During the same time frame as the increase in SSL C&C servers — January 2014 through December 2015 — the firm found that overall monthly malware occurrences were roughly stable, with just a slight upward trend. Comparing the two, Blue Coat found no single large-scale trend of rising malware use that would account for the growth in the SSL C&C method.

The firm also noted the timing of the increase in C&C servers came earlier than the appearance of associated malware, Softpedia stated. This is consistent with the idea of the bad guys building up a C&C framework in advance of launching a campaign for the holiday season. Indeed, the massive jump in C&C servers can be attributed to the malware utilizing domain generating algorithms (DGA) for short-living domains to build out a C&C infrastructure.

Whatever the reasons for this spread of this technique, however, malware is adopting SSL cloaking at an alarmingly high rate.