Why do random people ask me to add them on my yahoo messenger? Could it be spam?

Yes. It is spammers. Just ignore them.

If it's random and you obviously don't know them, then don't add. Could be viruses, spam etc.

yep it's spam just ignore them, accept only if you know the person.

Yes that is the very definition of spam

I think so. Might be a spam. But who knows. The spam might be the person that you know in the past in your life. So, anything can happen. But its better for you to ignore. Because you don't know these person who or what he or she is. So... just do other things rather than accept their add to you. Okay?

It can be spam if it is too random, or it can be people searching for the meaning of your nickname. The good thing is, it's up to you whether to add them or not.

They just wanted to join your messenger list, so yes they can be spammers. They can also unleash viruses on your computer if you click on the links they provided. It would be best if you only add your acquaintances and family members to your list instead. Just ignore the others.