Space.com verifies the dangerousness of directly looking at the Sun.
It states, “As Venus passes in front of the sun, the planet will cover only a small fraction of the solar disk, which means observers need to protect their eyes. It is very dangerous for humans to stare at the sun (even mid-transit) without proper eclipse glasses or solar filters for binoculars and telescopes.”
And, “To observe the sun, dense filters are used to block damaging rays. The only safe filters are #14 welder's glass, which is sold in specialized welder's supply stores. Special eclipse glasses are also available from telescope stores and astronomy clubs (they should only cost a couple of dollars).”