I have my own comment system with some rudimentary spam protection. Recently I started getting a few comments that appear to be automated with the name XlsUoIGh and the content doors.txt;10 I deleted the first set of comments, thinking it was probably nothing. However, they came back. They're constrained to one page and usually only 2 or 3 are posted. I've heard online that this text serves as a bookmark for future spammers to find and use. Is this true? I've also heard of similar pieces of content being posted like door.txt;6 What does the number mean? 
Why am I getting random comments with just door.txt;10 as the content?
spam;spam prevention;comments