Gibberish comments

On three seperate postings I received three long comments that appear to be pure gibberish. Likewise sender’s name and email address. One such reads as follows:
VygFSN tdeqlvdmtuuf, [url=http://nrqxehthufyk.com/]nrqxehthufyk[/url], [link=http://ajkqnflgmalz.com/]ajkqnflgmalz[/link], http://hjarjytazgde.com/
Any way to avoid future attacks?
Motivation of sender?