I have three fast-growing hogweed plants in my backyard, but a garden designer at City People’s warned me not to tackle them before consulting someone at the Center for Urban Horticulture. She said hogweed is nasty, and it certainly looks so.
If you do have hogweed (Heracleum mantegazzianum), it is a Class A noxious weed (eradication required by law in King County and the State of Washington). You should contact the King County Noxious Weed Control Program to report it using their Infestations Form.
The folks at City People’s were right to tell you not to touch it, as the sap is considered a public health hazard. Any skin exposed to it will become extremely sensitive to sunlight. King County provides more information about the effects.
You can find out more about the history of this invasive in North America (including a song!) at the site E-Flora B.C.