The crime reporter, who works for a national newspaper, received two threatening phone calls after Ryan sympathisers placed her mobile phone number and other personal details on a memorial website last night.
Photos of the reporter, along with her email address, were also posted on the website, which led to thugs ringing her phone and threatening to kill her.
When the reporter became aware that her personal details had been posted online, she immediately contacted gardai.
A source said: "This is being taken extremely seriously -- the journalist has given a full statement to gardai.
"A patrol car with armed detectives was placed outside her Dublin home last night. She will be given all necessary protection."
The journalist's partner told the Herald: "This is very worrying, of course it is, but she will not be intimidated by these people. She has already received two death threats on the phone and gardai are taking this very seriously."
The reporter has written a number of articles about Alan Ryan since he was murdered in Clongriffin, north Dublin, in September.
In the last of these pieces she wrote about a fundraiser for the slain RIRA man which was held last month in the Submarine Bar in Crumlin in which she revealed that Celtic and Ireland football star Anthony Stokes (24) had attended the event.
This article seems to have particularly angered Ryan's associates, who took to the internet last night to post vile comments about the reporter.
At least one comment suggests that Ryan's sympathisers should find out where the reporter lives.
The threats against the reporter come as gardai investigating Ryan's murder rearrested a man in his 50s who was originally questioned about it just days after Ryan was shot dead. The man was picked up in north Dublin yesterday morning and is being quizzed at Coolock Garda Station.
Gardai had to seek a warrant to arrest him again after fresh information had come to light since his previous detention.
Sources say that "it is very possible" that the man, who works as a taxi driver, may face charges.
Detectives have been working on the theory that a number of northside gangs clubbed together to murder Ryan who had been involved in a particularly bitter feud with the gang led by the so-called 'Mr Big' of Irish crime.