As far as I am aware, there is no malicious content on the lock.net website. It is run partially by my son, partially by me, with one partition used by another family member. My reassurances probably shouldn't convince you there is nothing wrong, however no one else to my knowledge has had any issue (other than the occasional slow service or the site being off line for a while).
Does your Norton give any further information, maybe a log file that states the name of whatever was detected? If there is something amiss, I would want to fix it immediately. Meanwhile, if I download that file from the web site using the link quoted above, my own computer scanner detects nothing untoward, nor anything else that I have downloaded.