Anonymous Student Feedback: Moving forward from abusive comments I'm looking for some guidance from some senior/experienced academics situated in the teaching space.

As a relatively new lecturer (though I have some experience in lecturing in the past) I'm always looking for ways to improve my teaching. After doing a bit of research around how different lecturers etc approach student feedback, a number had stated that using anonymous feedback solicited during the semester can be really helpful. 

So following on from that, I put on my learning site an anonymous feedback form for students that could let me know how they think the unit is going and what could be improved. The idea behind this was to get real-time feedback that could be implemented throughout the course, instead of for the following year. 

I left this open since week 1, and perhaps that was my mistake. Despite barely being into week 2 (in which week 1 was just a basic introductory lecture to the course) one student has provided some anonymous feedback, which isn't feedback at all. Rather, it is just a string of abusive, sexist and foul language comments. 

Due the alarming nature of the feedback, I approached a mentor/supervisor about what I should do. They were conflicted, because on the one hand, the nature of the comments were highly inappropriate, abusive, and raise concerns about the safety of my person in my teaching space. However, no specific threat at this time was made. On the other, having anonymous informal feedback throughout the unit is a good way of getting students to reflect on their own learning experiences without the fear of being reprimanded re assessments, and help me improve my teaching in the process.  

I'm caught between continuing to allow anonymous informal feedback, or taking this option away and informing students of the reason. No other student has provided any feedback. Only myself and my teaching assistant have access to the feedback. Only students enrolled in the unit have access to the form. 

Experienced lecturers/professors, how would you handle this situation? 

This response here has been somewhat useful for future tips: 

What is the best way to solicit teaching feedback from students (before the class is over)?
It sounds like you've encountered the well-known downside of online disinhibition effect, more colloquially known as GIFT.  There is simply nothing that can be done to prevent some people from being horrible when offered anonymity.

So, let's parse out two different questions about how you should react: 1) what actions should you take to protect yourself and other students? and 2) should you continue to use the anonymous feedback form?

Let's start with the first question: given that you know there is a horrible person in your class, what should you do to protect yourself and other students?
I see three basic possibilities here, either a) the person is insincere in their statements and is trolling you to try to get a reaction, or b) the person is genuine but not a threat, or c) the person is an actual threat to the safety of yourself or others.  If you are concerned that it might possibility c), then if there is any way for your IT staff to penetrate the anonymity and investigate, it's reasonable to ask them to do so, just as if somebody had made a serious electronic threat through some other channel (your institutions likely will have a process for reporting serious threats of harm, though, which may mean you shouldn't start by going directly to IT).  Otherwise, it's probably best to ignore it and move on, because otherwise you're just giving them the reaction and power over your actions that they are looking for.

Now, turning to the second: should you continue to use the anonymous feedback form?  The one problem with true anonymity is that if you get more nasty comments, you can't tell whether they came from the same person or not. I would recommend looking into whether you can get pseudonymous information from your system, i.e., so that Student X's comments are all collected together and Student Y's comments are all collected together separately.  That way, you can separate out and discard feedback from the horrible person (essentially marking them with a "troll" filter), while still getting meaningful feedback from other students who have more positive disinhibition from the anonymity.

It's a pity that some people are horrible and try to screw things up for everybody else; the rest of us need to try to figure out how to appropriately protect ourselves and our institutions while keeping them from profiting from this behavior.