Walsall have apologised for a tweet sent to Wolverhampton Wanderers' Twitter account which branded their rivals "inbred b******s".
The League One club said their account had been hacked before the post was sent, but was later deleted.
Andy Butler's 69th minute goal was enough to give Walsall a shock victory at Molineux on Tuesday night, as Wolves suffered their first defeat of the campaign.
The tweet was screengrabbed by several users
"Our official account was hacked at 22:36 last night," Walsall said in a statement. "As soon as the club's Communications Team, who were at Molineux for the fixture, were made aware of the Tweet, it was deleted and an apology issued."
The club will launch a full investigation and promised the "strongest action" will be taken against the culprit.
Wolves responded: "We completely accept [Walsall's] explanation and this issue should not take shine off their victory last night. As far as we are concerned the matter is done and dusted."
Liverpool recently expressed their regret after the club's official Twitter account endorsed a message mocking the Munich air disaster, which claimed the lives of eight Manchester United players.