A 'right' to anonymity

One becomes accustomed to people hiding behind the anonymity of the internet from time to time (God knows, I can think of one time I did it to insult someone, drunkenly); this is why message boards on serious topics aren't always a good idea - but it's coming to something when people think they can pick up a phone and make serious claims about someone's professional integrity without being willing to disclose who they are.

That's the situation I experienced about half an hour ago, where a woman was making spurious claims of impropriety about a someone who's just recently left my place of work, and someone who I have a great deal of respect for. The conversation ended with me saying "and where is it you're calling from" to which the woman replied "I didn't say, and I don't have to" before hanging up. I must say it made my blood boil because if you're going to try and upset the applecart, rightly or not, you should at least have the courage to equal your conviction.