It's an overstatement to say that viruses are "unrelated to the rest of life". They have RNA or even DNA, which almost certainly makes them related.
If we found a living organism which didn't have RNA or DNA, that would be a good candidate for an alien. It would help if we found it on another planet though.
If we found a living organism which didn't have RNA or DNA, that would be a good candidate for an alien. It would help if we found it on another planet though.