The Yandex spider is a frequent visitor to one of the sites I manage. On ocassion it replaces the page name with two ampersands and a space. So if the page is:

/mypage.aspx?param=value 

then it will try and crawl it as:

/&& ?param=value  

Any idea why it is doing this?

[EDIT] If I remember correctly the IP that this "mistake" is coming from is based in California and not Russia. I believe that they crawl US sites from a US based IP address. Not sure if that helps.

More Info about request:
IP: 199.21.99.82
City: Palo Alto
State: California
Country: United States
ISP: Yandex Inc.
User-Agent: Mozilla/5.0 (compatible; YandexBot/3.0; +http://yandex.com/bots)