The trade-only car hire specialist said it took its systems offline as a precaution to protect agent partners and suppliers following the incident on Sunday (7 July).
Flexible said reservations were unaffected, with clients able to collect their vehicles without issue.
In an update issued to TTG on Thursday (11 July), the company said its systems were "back up and running" but without access to certain countries.
"Throughout the day, more and more destinations will be uploaded and more functionality will be available to agents," said a spokesperson.
"We would encourage our agent partners to check our Facebook and Twitter pages for regular updates.
"We appreciate their continued support and apologise for all the inconvenience this has caused."