snuck / sneaked
The past of sneak.
Sneaked is the standard past tense and past participle of sneak, as in He sneaked out and He has sneaked out.
Examples
Use She sneaked past the guard. (past tense of sneak)
Avoid She snuck past the guard. (a variant of sneaked)
Snuck is now common in American English, and dictionaries list it. However, many people still consider snuck an error and judge the speaker who uses it.