FBI investigating ballot drop box fires in Oregon and Washington

A fire was set in ballot drop boxes in Vancouver, WA, and Portland, OR, damaging hundreds of ballots. Authorities believe the incidents are connected and are searching for a suspect. The FBI is involved in the investigation, as this is a federal crime. Concerns about election security have been rising, with increased threats to voting locations and election workers. The Department of Homeland Security had previously warned about potential attacks on election infrastructure. Despite security measures, ballot drop boxes have been targeted by disinformation since 2020.

What concerns have been raised by the Department of Homeland Security regarding ballot drop boxes?

How have ballot drop boxes been perceived in terms of security before the 2020 election?