From the INDEPENDENT news "Muslim activists hack Isis mailing list hours after terrorists claimed it was unhackable" (highlighting by myself):
After numerous cyber attacks and official takedowns targeting its Amaq “news agency”, Isis issued a message on Friday night claiming it had increased security.
“In response to recent events, we have imposed more stringent security measures on our systems,” said the email in Arabic. “We can now handle email attacks or any type of hack.”
For a Muslim hacking collective called Di5s3nSi0N, which previously disabled the automated email service last month, it was “challenge accepted”.
As "it was" is already past and the automated email service had been disabled previously, showing respect to all my English grammar books, a Past Perfect form of "disable" should be used in the sentence highlighted boldly above. Why it is not?