The email account of Farhatullah Babar, the spokesman for President Asif Ali Zardari, was hacked soon after Haqqani resigned as Ambassador to the US on Tuesday night, sources told PTI.
The email account was then used by the hacker to send a message to some persons with what the hacker claimed was the "real memorandum" purportedly delivered to former US military chief Admiral Mike Mullen.
Haqqani was asked to resign by the Prime Minister after he was linked to a secret memo sent to Mullen by Pakistani- American businessman Mansoor Ijaz.
That memo has been released to the media by Ijaz.
Babar contacted the head of the Federal Investigation Agency and asked him to look into the hacking of his email account.
FIA experts were able to restore Babar's account several hours later.
Investigators are now trying to trace the hacker, sources said.
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