Here's an indication:
From February to April 2008, the PMO did not receive many of the mails addressed to it because of the virus. The extent of the damage is uncertain.
The problem was detected late last April after which the Microsoft Outlook Express software, on which the PMO’s email communication system was based, was replaced with SquirrelMail.
The matter came to light during one of the hearings of the Central Information Commission where the PMO submitted that there was a virus problem in the months of February, March and April “that was finally diagnosed only late in April”.
I guess there are many possible angles to this story, but I'll take the good one about the PMO replacing Outlook Express with SquirrelMail.