Karen "Gary" Kazaryan, 27, was arrested Tuesday by the FBI.
Prosecutors said he hacked into the women's Facebook, email or Skype accounts between 2009 and 2011 and changed their passwords so they were locked out.
He then searched their accounts for naked or revealing photos of themselves or their friends, according to court filings.
Kazaryan then contacted the friends and threatened to post those photos unless they showed him their breasts on Skype, a service that offers live video chatting, the FBI said.
When some women refused, court records say, he posted the nude photos on Facebook.
In one case, the court filing says, two women showed their breasts while crying so he would take down the Facebook photo.
One woman told a friend the experience made her feel as if she'd been raped, and both those women said they were afraid to use a computer or be home alone, according to the FBI.
At least one of the victims had a Cal State-Northridge email address, according to an affidavit filed in court by an FBI agent.
A grand jury handed down a 30-count indictment Friday, which includes 15 counts of computer intrusion and 15 counts of aggravated identity theft.
Kazaryan, who lives in an apartment on West Stocker Street, was charged with rape and other offenses in 2008, according to state court records. The charges were dismissed in 2011.
Los Angeles Police Department records show he was arrested in January 2012 on suspicion of possession for sale of marijuana. Those charges are pending.
The U.S. attorney's office in Los Angeles said Kazaryan victimized more than 350 women, though the FBI hasn't identified all of them. He had about 3,000 pictures of nude or partially clothed women, either ones he'd taken from their accounts or ones he'd taken himself via webcam, prosecutors said.
The FBI said anyone who might have been a victim should call them at 310-477-6565.