This was interpreted by Twitter as a hyperlink because it automatically recognises the letters after a full stop as representing an established top-level domain (TLD) name. The former New York City mayor reacted in outrage, claiming that the so-called "committed card-carrying anti-Trumpers" at Twitter had "allowed someone to invade" his tweet.
How was the link created?
The move infuriated Giuliani, the Post reports, who again took to Twitter to complain that "Twitter allowed someone to invade my text with a disgusting anti-President message", Giuliani tweeted, adding that the "same thing-period no space-occurred later and it didn't happen".
When Jason Velazquez, 37, who owns a web design firm in Atlanta, saw the tweet, he immediately bought the domain for about $5.
Giuliani's orginal tweet had included a second punctuation error, he reasoned, but that hadn't resulted in a link.
Bush's final journey: By motorcade, plane and train
Bush will then be returned to Houston for burial Thursday at his presidential library at Texas A&M University. The couple was married for 73 years, longer than any other United States presidential couple.
At most, Velazquez thought his stunt would get a "few hundred retweets" and then be absorbed into the Twittersphere, but by early Wednesday morning, Giuliani's tweet containing the link had about 45,000 likes and almost 17,000 retweets. Giuliani has served as President's Trump's lawyer, and also as his cybersecurity advisor.
Rather, Giuliani accidentally activated an automated Twitter feature that applies to everyone's tweets, whether they're liberal or conservative.
A Twitter spokesman balked at the claim, telling The New York Times "the accusation we're artificially injecting something into a tweet is completely false", adding that Twitter is actually created to prevent tweets from being edited.
So why doesn't he just delete the tweet?
Velazquez told The Post that Giuliani's follow-up tweet "speaks to the impulsive nature of the administration where they're not thoughtful in anything they put out there, especially on Twitter".
It would be the simplest option, but as of Thursday Mr Giuliani's tweet - which has been liked more than 47,000 times and retweeted more than 17,000 times - is still up. "Either I affect what his message is, or I affect what his message is", he said.