Ukrainian startup Semalt is running a botnet generated by malware that is hidden in a utility called SoundFrost. Semalt bots access hundreds of thousands of websites, sending out requests with synthetically generated referrer headers. Each of these headers contains the website URL the perpetrators are trying to give an SEO boost. The referrer spam creates backlinks to a certain URL by using publicly accessed logs. In Google Analytics, this is classified as human traffic. In the last 30 days, Incapsula saw Semalt botnet attempting to access over 32 percent of all websites on their services.”]
Source: https://informationsecuritybuzz.com/news/incapsula-blocks-semalt-referrer-spam-botnet/