"It's confirmed what we've been thinking for a while, that tweeting can be the basis of a defamation case ... but I've always thought he was going to win," Professor Cheer said.
In order to defame a person, someone must lower the opinion of another in the minds of right-thinking members of society.
The everyday ramblings and insults thrown around on Twitter would not be enough to form the basis for a defamation suit, but serious accusations or lies which could be construed as truth posted on the site could be, Professor Cheer said.
"You need to stop and think before you tweet something about someone else - are you hurting their career or their personal lives because you could be defaming them."
Special counsel for Duncan Cotterill Lawyers Jonathan Forsey said the "informality and truncated nature" of social networking sites afforded no protection.
"Modi has already indicated that he will be filing an appeal ... so this may not be the last word in the matter, but the reasoning behind the jurisdiction and publication analysis in this decision is likely to be followed by New Zealand courts," Mr Forsey said.
Meanwhile, Cairns has spoken about being vindicated after the case dragged through the courts for almost 2 years.
He said the victory came with "mixed emotions".
"I feel sad that I've had to go through this process to clear my name ... But then obviously joy in the fact that we've come through on the right side," he told TV3's Campbell Live.
At times, he questioned his decision to sue Modi, Cairns said.
"But the main thing was that we got the right result."
The eight hours for which he was questioned by Modi's lawyer, Ronald Thwaites, QC, who called him a liar 24 times in his closing address, was "one of the hardest things, if not the hardest thing" he had ever been through.
Cairns' mother, Sue Wilson, said his first words to her when he broke the news were: "I can't believe I have beaten such a big guy."
