John Wilson invited John Evans to his flat to confront him about his suspicions.
However, the unemployed 36-year-old lost his temper after being ridiculed by the oil company analyst.
The High Court in Inverness heard that Wilson picked up a tomahawk-style axe from his bedroom floor and attacked Mr Evans from behind.
Advocate depute Iain Armstrong, prosecuting, said that the victim sustained a number of injuries, including a life-threatening depressed skull fracture.
In a statement, Mr Evans said: "He behaved like a crazy man."
Wilson, of King Street, Aberdeen, admitted assaulting Mr Evans to the danger of his life in January.
Defence advocate Colin Mackenzie told Lord Kirkwood that his client's brother was a close friend of Mr Evans.
All three men were interested in computers and Mr Evans agreed to link the two brothers' computers together.
Easier access
However, Wilson then began to suspect that someone was hacking into his machine.
His suspicions were heightened when he discovered that a software disc provided by Mr Evans contained a hidden file which gave an outsider easier access to his computer while he was on the internet.
Wilson became convinced that Mr Evans was the hacker when he noticed that his computer would behave normally when Mr Evans was out socialising or at work.
"Wilson decided to confront Mr Evans about this and invited him to his flat," said Mr Mackenzie.
"By this time he had become extremely upset and certainly intended to have words with him about the hacking."
However, his client maintained that he had not planned to attack Mr Evans.
"He confronted him about the hacking, and was met with a degree of ridicule," said Mr Mackenzie.
"He became very angry and suffered a loss of self control, and unfortunately there was in the immediate vicinity, lying on the bedroom floor, an axe with which he had been lifting metal carpet strips at his flat doorways."
Mr Mackenzie claimed that his client had held the hatchet by the head and used the handle to hit his victim.
Sentence was deferred until later in the month for psychiatric, social and community service reports.