Viruses sense chemical signals left behind by their forebears so they can decide whether to kill or just to infect their hosts.The discovery—in viruses that attack Bacillus bacteria—marks the first time that any type of viral communication system has ever been found. But researchers say that many other viruses could communicate with each other through their own molecular languages—perhaps even viruses that are responsible for human diseases. If that is the case, scientists might have found a new way to disrupt viral attacks. A viral invader of Bacillus bacteria—a phage called phi3T—makes a chemical that influences the behaviour of other viruses.
— source scientificamerican.com