Like mobsters, cells keep their friends close and their enemies — at least some of them — closer. According to new results from HIV researchers, one way that human cells prevent certain viruses from raging out of control is by blocking new viral particles from ever leaving an infected cell’s surface. And, they believe, HIV thrives in part because it has evolved the ability to get around this obstacle. Viruses can only reproduce using the mechanisms and material of their hosts. Some of them — the so-called “enveloped” viruses, which are encapsulated inside a lipid membrane — assemble at the host cell’s outer membrane and then bud off during their release.