[Harry_p]

Where did the overspray come from and what sort of paint is it?

If it's from something which was painted nearby with an aerosol then cellulose thinners on a cloth will get it off pretty quickly, assuming your car has modern and well cured paint it won't cause any harm ( test on a small hidden area first! )

Don't use any pressure, literally just wipe it over and wipe it off. If it's working properly you shouldn't need to use pressure or scrub at it. Just change cloth when it starts to get clogged and isn't removing as effectively.

 

[Harry_p]

Agree totally, proper body shop paint will need mechanical removal, start with clay then polish. If really bad it may even need wetsanding but you shouldn't be expected to do that.

 

[Harry_p]

Proper paint shops will (usually) use a 2k or two part paint which cures by chemical reaction. 1k, solvent based paint like you'd find in aerosols or older cellulose based paints relies on the solvents evaporating out to dry, adding solvent to them re-wets them so they can be removed.

You have to be careful when using thinners as it can harm some older paints, but in some circumstances it's the quickest and easiest way to remove fresh solvent based paint from a car.