HIV virus particles cannot pass through condoms so they provide excellent protection from HIV if used CORRECTLY and CONSISTENTLY. *CORRECTLY* means putting the condom on BEFORE genitals come into contact and as soon as you think you may have sex. This is because vaginal and penile fluids released even before climax contain the HIV virus. *CONSISTENTLY* means using condoms correctly EVERY TIME you have sex. This is because you can get HIV from having unprotected sex even one single time.
Attribution: Marie Stopes