The "animated singing virus" was probably Leonardo Da Vinci, which was based on the real-world panic surrounding the "Michelangelo" virus in 1992. Michelangelo displayed on the infected machine's screen a still image of the artist Michelangelo's Sistine Chapel fresco, much like the fictional Leonardo virus displayed a solarized Vitruvian Man. Some viruses of the era (early 90s) did feature animation, such as making the on-screen text slowly disappear or "rain down" the display like the Matrix intro.
Not animated but I have been struck by the music bug virus[1]. Given hacker's egos and sense of humor I wouldn't be surprised for a moment by a animated singing virus.
Maybe not, but you're damn right I've rickrolled hackers trying to access our servers and steal user data.