Viruses definitely know how to throw a party in a host cell, but it has recently been observed that host cells seem to leave some viruses a parting gift.
Upon infecting a host cell, viruses will hijack machinery inside the cell to make copies of themselves. When they are all done, viruses will leave the first host cell to find another host cell to “infect” and yada yada yada, the process will start all over again. Usually that first host cell is left in sad shape but will display parts of the virus to try to flag down cells in the immune system. At this point in the infection, the immune system is just scaling up for a war and is trying to play catch up with these pesky invaders which have likely moved on to another location in the body.
Now it seems that host cells have found another way to hinder a viral attack; some host cells can leave a parting gift, an antiviral molecule, inside the exiting virions. Like a goody bag gone wrong, this antiviral molecule will immediately alert the immune system should the virus try to infect another host cell.