The modem attached to Sheldon's computer was a Tandy DCM-212 1200 baud modem which was introduced in 1985. It was restored by David Murray, creator of "The 8-Bit Guy" YouTube channel, who provided its use for the show.
At the end of the episode, George refers to Missy as 'Slugger'. This is the same nickname that Penny's dad has for her (Penny) in The Big Bang Theory (2007).
Sheldon is having an altercation with an online user in a BBS, the name of that user is CICADA3301, the name of the real life hacking group.