Some bareback pornography studios say that they do not inquire whether their models are HIV positive, but assume that they are infected. For example, Hot Desert Knights (HDK) was one of the studios that initially operated on the assumption that all of their bareback models were HIV positive. However, in February 2008 HDK announced that it would begin testing its models for HIV and engage in a process of "sero-sorting", which match HIV-positive performers with other HIV-positive performers, and negative with negative. Critics suggest that sero-sorting may not prevent the development of a multi-strain HIV "superinfection". By contrast, BelAmi is one of the studios that claimed from the beginning to test their bareback models for HIV before allowing them to participate in condom-free scenes. A notice on the BelAmi website states: "all our performers are regularly tested for the presence of HIV or other communicable diseases."