Fans of the 34-year-old 'That '70s Show' star were left baffled when he seemed to post a string of bizarre updates, reported Radar online.
One tweet included a snap of him and his pop star girlfriend in bed together, with Lovato seductively biting his lip.
The image was originally leaked back in April.
After the updates, Valderrama logged in himself to explain to fans that an imposter had broken into his account.
He wrote, "Attention Everyone! Someone just hacked my twitter account."