There's X-Men #194 where this guy Pan created a method where he added mutant DNA to a virus which he would then infect himself with to give him the powers that the mutant has.

The super-soldier serum, it was revealed that the serum was a virus in the early 90's which explained why the serum never wore off like other drugs.

About Face, a virus that allowed the host to alter their own physical form according to their own wishes. Daredevil #319

Techno-organic virus.

Carrion virus, when it came to McBride that is, while the rest died.

An unknown virus that John Jameson got from a space walk that gave him superhuman strength.

An undetectable intelligent metal nano-virus from Peter Parker: Spider-Man #48 that was designed to enhance latent human/mutant tendencies for application in military conflicts.

Extremes virus from Iron Man.

Marvel Zombie virus. The ability to move, talk, and think while dead is in a way a power.