Any other year, a sunny lunch hour in October in Boston's financial district would see Post Office Square jammed with people.But the slow return from the shutdown of March and April has not caught up to pre-pandemic levels of movement. 5 Investigates analyzed mobility data from our cellphones, looking at people's movements in counties in eastern and central Massachusetts. The drop in mobility is dramatic in March and April, followed by a slow increase beginning in May. Levels are fairly steady in September and so far in October. Between counties, the difference can be significant, for example comparing more rural Plymouth County with denser Suffolk County. "I think Massachusetts is definitely on the move again," said Dr. Satchit Balsari, an assistant professor at Beth Israel Deaconess Medical Center and the Harvard T.H. Chan School of Public Health.He's studying how mobility data should be used to fight COVID-19, and said the mobility data is a starting point for further analysis."We have to be very careful about how we interpret this data," he said. "Are you missing how the most vulnerable, the poor, the elderly from the perspective of this pandemic? And are we actually not counting them by relying on these mobility data?"There are also privacy concerns."They provide rich information. These are data off the people they should be accessible to scientists. But we have to be extremely careful and go that extra mile or two to ensure that the best privacy preserving algorithms are instituted," Balsari said. Paul Roberts, editor in chief at the Security Ledger, a cybersecurity publication, said privacy can be protected while using the cellphones to fight the spread of COVID-19."There's no evidence of any sort that any of that data has been mishandled, misused, abused, given to the private sector or anything like that," he said.Some states and countries are using mobility data to conduct digital contact tracing, allowing cellphone users to be alerted if they've come in contact with someone who's tested positive for COVID-19.Other countries have gone further."In South Korea, mobile applications were used to enforce quarantines to make sure that people who had tested positive didn't leave their home or go out and become super spreaders," Roberts said. New York, New Jersey and other states recently launched apps to help with contact tracing.The Baker administration said in a statement: "Massachusetts continues to explore potential options surrounding COVID-19 automated exposure notifications, looking at new technology available and assessing early results in other jurisdictions."The Boston Globe has reported that the Baker administration has admitted to lawmakers that they don't know where approximately half of COVID positive cases were infected from. A spokesperson from the state said those cases were not "tied to a specific cluster," but wouldn't elaborate. "What we really want to see is a really strong federal public health response that says, listen, we've got these devices that can be hugely useful in monitoring and managing this disease and preventing disease spread within our society. And we can do it in a way that preserves privacy, preserves data security and helps keep people safe," Roberts said.