Scientists have found an "invisibility cloak" that allows the Aids virus to lurk unnoticed in human cells after infection and replicate without triggering the immune system.
And they've managed to "uncloak" the virus with an experimental drug in lab-grown cells - a feat that may lead to new and better HIV treatments, the team wrote in the journal Nature.
"The hope is that one day we may be able to develop a treatment that helps the body to clear the virus before the infection is able to take hold," the study's lead author Greg Towers of the University College London said.
The body's immune system is the first line of defence against infection, with an "alarm system" in each cell for detecting invading bacteria or viruses.
When the alarm is triggered, the cell activates an anti-viral response and alerts surrounding cells, which do the same.
But the human immunodeficiency virus (HIV) infects vital white blood cells of the immune system and replicates undetected for a while before triggering the alarm system - a trait that scientists have battled to understand.
"HIV is extremely adept at hiding from our body's natural defences, which is part of the reason the virus is so dangerous," said Towers.
"Now we've identified the virus' invisibility cloak and how to expose it, we've uncovered a weakness that could be exploited for new HIV treatments."
Towers and a team identified two molecules inside human cells that are "recruited" by HIV after infection to help shield it and thus delay the immune response.
They then administered an experimental drug, based on Cyclosporine, which is widely used to prevent organ rejection in transplant patients because it dampens the immune system.
The drug prevented the virus using the molecules as a cloak, they found.
"The team used a modified version of the drug, which blocks the effects of the two cloaking molecules without suppressing immune activity," Towers said.
HIV is a retrovirus, inserting its DNA into the genome of CD4+T cells and turning them into virus factories.
Some 35.3 million people around the world are living with HIV, which destroys the immune system and has caused more than 25 million deaths since Aids first emerged in the early 1980s, according to the World Health Organisation.
Existing treatments help infected people live longer, healthier lives but do not cure Aids. Many people in poor communities do not have access to the life-giving drugs, and there is no vaccine available.