They have beef with each other but annie dislikes vivi even more because he has to share the computer with vivi and vivi TOTALLY stole his hair dye style
annie IS scareware but he doesn't do seriously malicious until he meets vivi... but he has access to exploits and backdoors, so just malware... i'll come up with a specific classification later
Annie on the other hand works in the background, luring MC into a false sense of security believing that annie is actual antivirus software. Only after vivi shows up does annie become malicious
Vivi is extremely shameless and makes no actual effort to hide the fact he is a virus after you find out he's malware. His full name even states it. Virus Trojan, lol...
specifically he's rogue security software, and both of them are malware however annie is trying to be more secretive about it (and his name is mostly a mystery...)
ht19/ft19 are named 19 because of phuong's nickname, however pda19 has 19 for no other reason but to distinguish itself between playdate & pdlk if needed