A 36-year-old woman was groped by an unknown assailant Wednesday in Springfield, and Fairfax County believe the incident may be the 11th in a series of similar assaults, officials said.

The victim told police that a man came up from behind and groped her near the intersection of Amherst and Cumberland avenues about 1:20 a.m., authorities said. The man then fled. Police said that he was described as about 5 feet 9 to 5 feet 10, and that he wore a black t-shirt, khaki pants and a blue hat.

Authorities have been investigating a string of similar attacks in the Springfield area since early September.