Yahoo mail deletion problem?

ok here is what happened.I was in in my inbox reading an email when all te sudden all my mail all like 100 email when to my trash so my first thought was I don'tt want to lose allof them because there are some of them I needed so I went to get my son because he is better with the computer then I am and when I came back all the items were gone out of trash as well.Now my question is one would a virus be able to do that and if it did what is the probability that that's what made that happen or what else could have made all my email go proof and will it happen again?