Large botnets are broken down into smaller ones.

Researchers at F-Secure report that cybercriminals reduce the size of their botnets in order to make it more difficult for companies specializing in information security software to monitor and hinder the work of botnets.

Computers infected with a virus become so-called. "Zombies" in the botnet - a network that is used to send spam and to conduct attacks on other machines. An army of zombie machines can be controlled remotely, and, as a rule, their creators usually try to create the largest botnet for conducting custom DoS attacks.

However, researchers from the antivirus company F-Secure noticed that large botnets are broken up into smaller ones, since the creation of large botnets does not increase the profits of cybercriminals. Now, of course, the old large botnets continue to “work”, but the virus writers who create botnets at the moment do not try to make them large, since one large botnet does not give more money than a handful of small ones.
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In addition, cybercriminals simply began to fear that at one moment the central control server of such a large botnet would fall and the entire network would be lost.

Another factor highlighted by F-Secure is that virus writers have become lazier (other coders are also concerned?) And are not trying to create non-standard, "elusive" antivirus software viruses.