Is sharing your internet connection is a security/privacy risk?

I'm curious if sharing your internet connection is a security/privacy risk? One of the users on my connection is not as security/privacy minded as me. I have a cable modem which goes into a switch and my 2 computers are plugged into the switch. This gives different ip addresses to the computers so in theory it should look different to outsiders?

Obv my isp knows it's same connection but I'm curious if other parties like websites or programs on my computers can somehow tell it's the same, and if my privacy can be jeopardised in that way. Also besides the privacy issue curious if having a computer on this connection in the above mentioned setup (modem+switch), that isn't as secure minded as me can compromise my security. Or am I worrying too much?

 

Do you have a switch or a router ? Most people use routers, because they hide the PCs connected with an internal non-internet routable ip address. Ip addresses that are internal only are 192.168.x.x, 172.16.x.x to 172.31.x.x, and 10.x.x.x

I'd say sharing a switch with your friend is risky. Because worms can navigate and spread through shared networks. I rent a room out and provide internet access, but the renter is separated in his own VLAN. He once gave me a document to print using my printer, and his USB memory stick was infected. Then my intrusion detection system detected remote admin traffic to his machine. And he uses most of my bandwidth downloading pirated movies. He finally decided to get another phone line and his own DSL connection, thank goodness.