“Pushdo” affected 4.2 million IP addresses four million computers.
Malevolent bot traffic spiked last year at eight billion, doubling as a percentage of all web traffic from 12.25% to 23.6%, according to a report from Distil Networks.
The US emerged as the largest source, sending out 47% of the bots, with the UK second at 19% and Germany third with 10%
Mobile bad bots are a prevalent threat, reportedly running on 9 out of top 10 mobile operators and more likely to be found in USnetworks than any other.
More than 1,100 ISPs and hosting providers serve bad bots as 70% or more of their total traffic, especially between 6pm and 9pm ET.
The most prevalent bot during the year was "Pushdo", which affected 4.2 million IP addresses.
In terms of ISPs, Verizon Business and Level 3 Communications said to have served most of the bot traffic, being responsible for 11%and 10% of all bad bot traffic respectively.
Distil Networks said: "The number of bad bots has grown exponentially in recent years, causing varied levels of harm to all Internet stakeholders."
"Individual Internet users experience poor performance and often lose control of their own connected device; businesses see their online intellectual property, content, and data stolen while facing unnecessarily high bandwidth fees; and any organization or person who relies on one or more websites to perform its mission increasingly faces bot-driven obstacles to success."
Good bots on the other hand dropped as a percentage of all web traffic from 27.25% during previous to 19.4%.