Apart from the beneficial clinical effects of HAART, treatment advances may have unintended effects on sexual behaviour. Evidence suggests that since HAART became available, the prevalence of unprotected sex and the incidence of sexually transmitted infections including HIV have increased, mostly among men who have sex with men (MSM). Some HIV positive persons receiving HAART, especially those with a undetectable viral load, may feel protected from transmitting HIV sexually. Recent evidence does suggest that an undetectable viral load may reduce the level of infectiousness of HIV positive persons receiving HAART.