IMAP Missing Emails

Hey folks

I have a friend who has several computers set up for email access for two different email accounts, all using IMAP.

Lately, email has begun to disappear. She things its a virus, I think its something else. The only thing I've come up with is someone has stolen her usernames and passwords, and has evilly deleted the mail... doesn't make a lot of sense, but that's what I'm left with.

Has anyone experienced any odd, weird, and unexplained behavior pertaining to mail being deleted with IMAP and Mail?