Trolls targeted people with epilepsy on Twitter with seizure-inducing videos, according to the Epilepsy Foundation.
The US charity said the perpetrators had posted flashing and strobing Gifs and videos in November.
The Epilepsy Foundation's own Twitter handle and hashtag had been used in order to target people with epilepsy, it said.
The foundation has made a criminal complaint and requested an investigation.
Legal advocacy director Allison Nichol said: "These attacks are no different than a person carrying a strobe light into a convention of people with epilepsy and seizures, with the intention of inducing seizures and thereby causing significant harm to the participants.
"The fact that these attacks came during National Epilepsy Awareness Month only highlights their reprehensible nature.
"The foundation is fully cooperating with law enforcement and intends to utilise all available avenues to ensure that those responsible are held fully accountable."
About 3% of people with epilepsy have photosensitive epilepsy, which makes them susceptible to flashing lights at certain intensities or certain visual patterns.
In the UK, about 20,000 people have the condition and it is more common among children and teenagers.
TV regulator Ofcom demands TV programmes display flashing-light warnings.
And the UK's Epilepsy Society said in April that the government should require social-media companies to display similar warnings as a growing number of people were having seizures triggered by flashing images on platforms such as Twitter and Facebook.
"When it comes to deliberately targeting people with epilepsy with the intention of causing a seizure, we need to call that behaviour what it is - a pre-meditated and pre-planned intention to assault," said chief executive Clare Pelham said.
"The government must bring this behaviour within the reach of the criminal law."
However, the Epilepsy Society added smartphone displays, modern computer monitors and TV screens were less likely to trigger seizures than older equipment with a slower screen-refresh rate.