Disorganized serial killers are usually far more impulsive, often committing their murders with a random weapon available at the time, and usually do not attempt to hide the body. They are likely to be unemployed, a loner, or both, with very few friends. They often turn out to have a history of mental illness, and their modus operandi (M.O.) or lack thereof is often marked by excessive violence and sometimes necrophilia or sexual violence. Disorganized serial killers have been found to have a lower mean IQ than organized serial killers, at 89.4. Mixed serial killers, with both organized and disorganized traits, have an average IQ of 100.9, but a low sample size.