The advent of synthetic biological systems in the 21st century and the evolution into advanced nanotechnology has unleashed a very powerful weapon - Meme based viruses for humans.
As cyberwarfare was the real danger in the early 21st century, the beginning of the 22nd century opened up technology where viruses could be developed that could infect the human mind and alter behavior.
While Bio-crimes involving genetic engineering, deliberate infection of people with contagions and the like was a reality for terrorism in the 21st century (and by government sanctioned experiments in the 20th), the technology became more accessible in the 22nd century.
Both bateria and viruses could be manufactured in small labs that could alter human behavior. Subjects could easily become more passive or aggressive, generous, rude etc - all fairly basic emotional behavioral changes.
Several incidents often targeting a church, community group or even certain office buildings have happened in Asia, the USA and Europe, mainly led by extremist groups as a statement. A few incidents caused riots and a few homicides.
The US Department of Homeland Security and similar agencies carefully monitor water supplies, water cooler and other common vector points for spreading such contagions.
Vaccines have been developed for many of the common biological vectors used, and simple sterilization, filter and detectors are easily available to the public.
Conspiracy theorists often blame the government for using thee techniques, but no solid proof exists that governments have been using it on their domestic populations.