https://support.symantec.com/en_US/K9WebProtection.html Sad to see this go, it has been my web filter of choice for years now.
Yeah, this is sad. I hate to see decent free programs disappear. I am actually surprised it took this long for Symantec to terminate it after buying it 3 years ago. Symantec has a long history of buying up competing products, then kicking them (and their loyal users) to the curb. So I find it typical of Symantec to kill off this free product then suggest one of their expensive alternatives. In this case, Norton AntiVirus Plus for $39.99 per year! But look! They are even deceiving K9 users by suggesting they are being given a generous $20 discount by charging (their bold emphasis ) "only $39.99" to K9 subscribers when that's the price everyone can get as seen here. Norton/Symantec make good products. I'll give them that. But their strong-arm business practices and product pricings - at least for non-commercial home users - is why I will never recommend them.
Many people used K9 for content filtering, AKA parental control, and I don't think you can get that feature from Norton AntiVirus Plus. Last time I checked, you needed to buy Norton Premium. People are suggesting Kaspersky Safe Kids as an alternative. It is a standalone program, and has a free tier, and does a good job of filtering.