The Internet has revolutionized the dissemination of misinformation. Easy availability of incorrect information, gullible and eager masses, and ease of sharing has created fertile conditions for misinformation epidemics.
While a fair proportion of misinformation is likely created deliberately, it may well spread inadvertently. Misinformation that people carry is often no different than fact to them. People are likely to share misinformation with the same enthusiasm as they would fact.
Attitude congenial misinformation is more likely to be known (and accepted as fact), and more likely to be enthusiastically shared with someone who shares the same attitude (for social, and personal rewards). Misinformation considered useful is also more likely to be shared, e.g. (mis)-information about health related topics.
The chance of acceptance of misinformation may be greater still if people know little about the topic, or if they have no reason to think that the information is motivated. Lastly, these epidemics are more likely to take place among those less familiar with technology.