Don't remembering see this on my url before "?v="

I am not sure what this is from, but I don't remeber having this value /?v=alkjdafkl2 at the end of all my urls.

I recently added a new payment gateway plug-in, but can't see why it would be doing this.

Is some sort of tracing built into wordpress? Or something that is malicious and I need to worry about it?